210 Short question answer on P block elements

25 short question-answer on Group 13 elements

Basic Concepts

Q: Which elements belong to Group 13 of the periodic table?
A: Boron (B), Aluminium (Al), Gallium (Ga), Indium (In), and Thallium (Tl).
Q: What is the general electronic configuration of Group 13 elements?
A: ns²np¹
Q: Why is boron classified as a metalloid?
A: Boron exhibits both metallic and non-metallic properties.
Q: Why does aluminium have a lower density than expected?
A: Due to its low atomic mass and high metallic bonding leading to a less compact structure.
Q: Which element in Group 13 shows the highest metallic character?
A: Thallium (Tl).

Physical Properties

Q: Why does boron have a high melting point?
A: Due to its strong covalent bonding in the crystalline structure.
Q: Which Group 13 element has the lowest melting point?
A: Gallium (Ga), because of weak metallic bonding.
Q: What is the oxidation state of Group 13 elements in most compounds?
A: +3
Q: Why does thallium show a stable +1 oxidation state?
A: Due to the inert pair effect.
Q: How does the ionization energy trend vary in Group 13 elements?
A: It decreases down the group but Ga has slightly higher IE than Al due to poor shielding by d-electrons.

Chemical Properties

Q: What happens when boron reacts with acids?
A: Boron does not react directly with acids due to its non-metallic nature.
Q: Why does Al react with both acids and bases?
A: Because it is amphoteric in nature.
Q: Write the reaction of aluminium with sodium hydroxide.
A: $2Al + 2NaOH + 6H_2O → 2Na[Al(OH)_4] + 3H_2$
Q: Which Group 13 oxide is amphoteric?
A: Aluminium oxide ( $Al_2O_3$ ).
Q: What is the nature of boron trihalides (BX₃)?
A: They are Lewis acids due to the electron-deficient boron.

Compounds of Group 13 Elements

Q: Why is boric acid considered a Lewis acid?
A: It accepts a pair of electrons from water molecules.
Q: Give the formula of diborane.
A: $B_2H_6$ .
Q: What is the hybridization of boron in $BF_3$ ?
A: sp²
Q: Why is $BF_3$ more stable than $BI_3$ ?
A: Due to strong back bonding in $BF_3$ between boron and fluorine.
Q: What is the structure of diborane ( $B_2H_6$ )?
A: It has a three-center two-electron (3c-2e) bond involving hydrogen bridges.

Miscellaneous

Q: Which Group 13 element is used in thermometers for measuring high temperatures?
A: Gallium (Ga).
Q: What is the role of aluminium powder in thermite reactions?
A: It acts as a reducing agent to produce molten iron.
Q: Which Group 13 element is used in semiconductors?
A: Gallium (Ga) in the form of GaAs (Gallium Arsenide).
Q: Why is aluminium corrosion-resistant?
A: It forms a protective oxide layer on its surface.
Q: Which compound of boron is used as a rocket fuel?
A: Boron hydrides (e.g., diborane, $B_2H_6$ ).

25 short question-answer on Group 14 elements

Basic Concepts

Q: Which elements belong to Group 14 of the periodic table?
A: Carbon (C), Silicon (Si), Germanium (Ge), Tin (Sn), and Lead (Pb).
Q: What is the general electronic configuration of Group 14 elements?
A: ns²np²
Q: Why does carbon show allotropy?
A: Due to its ability to form different structural modifications like diamond, graphite, and fullerenes.
Q: Which is the most metallic element in Group 14?
A: Lead (Pb).
Q: Why is silicon a semiconductor?
A: It has an intermediate band gap (~1.1 eV), allowing controlled electrical conductivity.

Physical Properties

Q: How does atomic size vary down Group 14?
A: It increases due to the addition of new electron shells.
Q: Why does carbon have the highest ionization energy in Group 14?
A: Due to its small atomic size and strong effective nuclear charge.
Q: Why does lead show a stable +2 oxidation state?
A: Due to the inert pair effect.
Q: Which element in Group 14 has the highest melting point?
A: Carbon (as diamond), due to its strong covalent bonding.
Q: How does the catenation tendency vary in Group 14 elements?
A: C > Si > Ge > Sn > Pb (decreases down the group).

Chemical Properties

Q: What happens when carbon reacts with oxygen?
A: It forms $CO_2$ or $CO$ depending on oxygen availability.

$C + O_2 → CO_2$ $2C + O_2 → 2CO$

Q: What is the hybridization of carbon in methane ( $CH_4$ )?
A: sp³
Q: Why is $CO_2$ a gas while $SiO_2$ is a solid?
A: $CO_2$ has discrete molecules, while $SiO_2$ has a giant covalent network.
Q: Write the reaction of lead dioxide with hydrochloric acid.
A:

$PbO_2 + 4HCl → PbCl_2 + Cl_2 + 2H_2O$

Q: What happens when tin reacts with nitric acid?
A: It forms metastannic acid ( $H_2SnO_3$ ).

Compounds of Group 14 Elements

Q: What is the structure of graphite?
A: Hexagonal layers with delocalized π-electrons, making it a good conductor.
Q: Why does diamond not conduct electricity?
A: Due to the absence of free electrons, as all valence electrons are involved in covalent bonding.
Q: What is the nature of $CO_2$ in water?
A: Weakly acidic, forming carbonic acid ( $H_2CO_3$ ).
Q: What is the hybridization of silicon in $SiCl_4$ ?
A: sp³
Q: Why is lead (II) chloride sparingly soluble in water?
A: Due to its strong lattice energy.

Applications & Miscellaneous

Q: Which compound of silicon is used in waterproofing?
A: Silicones (Polysiloxanes).
Q: Which oxide of lead is used in storage batteries?
A: Lead dioxide ( $PbO_2$ ).
Q: Why is germanium used in transistors?
A: Due to its semiconductor properties.
Q: What is the commercial use of silica ( $SiO_2$ )?
A: Glass manufacturing.
Q: Why is tin used for coating food cans?
A: It is corrosion-resistant and non-toxic.

25 short question-answer on Group 15 elements

Basic Concepts

Q: Which elements belong to Group 15 of the periodic table?
A: Nitrogen (N), Phosphorus (P), Arsenic (As), Antimony (Sb), and Bismuth (Bi).
Q: What is the general electronic configuration of Group 15 elements?
A: ns²np³
Q: Why does nitrogen exist as a diatomic molecule ( $N_2$ )?
A: Due to its small size and strong triple bond between nitrogen atoms.
Q: Which is the most metallic element in Group 15?
A: Bismuth (Bi).
Q: Why does nitrogen show catenation less than phosphorus?
A: Due to weak N-N single bonds caused by strong lone pair-lone pair repulsions.

Physical Properties

Q: How does atomic size vary down Group 15?
A: It increases due to the addition of new electron shells.
Q: Why does nitrogen have the highest ionization energy in Group 15?
A: Due to its small atomic size and strong nuclear attraction.
Q: Which element in Group 15 is a liquid at room temperature?
A: None; however, white phosphorus melts at a low temperature (~44°C).
Q: What is the trend of electronegativity in Group 15?
A: It decreases down the group: $N > P > As > Sb > Bi$ .
Q: Why does nitrogen have a low boiling point?
A: Because it exists as a small diatomic gas with weak van der Waals forces.

Chemical Properties

Q: What is the common oxidation state of Group 15 elements?
A: -3, +3, and +5.
Q: Why is the +5 oxidation state of bismuth less stable?
A: Due to the inert pair effect.
Q: What happens when phosphorus reacts with oxygen?
A: It forms phosphorus oxides:

$4P + 5O_2 → 2P_2O_5$

Q: Why does nitrogen form strong hydrogen bonds in compounds like ammonia?
A: Due to its high electronegativity and small size.
Q: Write the reaction of ammonia with HCl.
A:

$NH_3 + HCl → NH_4Cl$

Compounds of Group 15 Elements

Q: Why is white phosphorus more reactive than red phosphorus?
A: Due to its strained P₄ tetrahedral structure.
Q: What is the hybridization of nitrogen in ammonia ( $NH_3$ )?
A: sp³
Q: Why is phosphine ( $PH_3$ ) a weaker base than ammonia?
A: Due to the lower electronegativity and larger size of phosphorus.
Q: What happens when nitric acid decomposes?
A: It forms nitrogen dioxide ( $NO_2$ ), oxygen, and water.
Q: Which oxide of nitrogen is neutral?
A: Nitrous oxide ( $N_2O$ ).

Applications & Miscellaneous

Q: Which allotrope of phosphorus is used in safety matches?
A: Red phosphorus.
Q: Which compound of nitrogen is used as a fertilizer?
A: Ammonium nitrate ( $NH_4NO_3$ ).
Q: Why is nitric acid a strong oxidizing agent?
A: Due to the presence of the $NO_3^-$ ion, which readily accepts electrons.
Q: Which Group 15 element is used in semiconductors?
A: Arsenic (As) in gallium arsenide ( $GaAs$ ).
Q: What happens when ammonia is oxidized in the presence of a catalyst?
A: It forms nitric oxide ( $NO$ ), a key step in Ostwald’s process:

$4NH_3 + 5O_2 → 4NO + 6H_2O$

25 short question-answer on Group 16 elements

Basic Concepts

Q: Which elements belong to Group 16 of the periodic table?
A: Oxygen (O), Sulfur (S), Selenium (Se), Tellurium (Te), and Polonium (Po).
Q: What is the general electronic configuration of Group 16 elements?
A: ns²np⁴
Q: What is the common oxidation state of Group 16 elements?
A: -2, +4, and +6
Q: Why does oxygen show a maximum oxidation state of +2 while others show +6?
A: Due to the absence of d-orbitals in oxygen.
Q: Which Group 16 element is a metalloid?
A: Tellurium (Te).

Physical Properties

Q: How does atomic size vary down Group 16?
A: It increases due to the addition of new electron shells.
Q: Which is the most electronegative element in Group 16?
A: Oxygen (O).
Q: Why does oxygen have a much lower melting point than sulfur?
A: Oxygen exists as $O_2$ molecules with weak van der Waals forces, while sulfur exists as $S_8$ rings with stronger intermolecular forces.
Q: Why does the metallic character increase down the group?
A: Due to decreasing ionization energy and increasing atomic size.
Q: Which is the most stable oxidation state of polonium?
A: +4

Chemical Properties

Q: Why is the -2 oxidation state more common in oxygen than in other Group 16 elements?
A: Due to its high electronegativity and small size.
Q: What is the hybridization of sulfur in $SO_2$ ?
A: sp²
Q: Write the reaction of oxygen with hydrogen.
A:

$2H_2 + O_2 → 2H_2O$

Q: Why does sulfur show catenation more than oxygen?
A: Due to stronger S-S bonds compared to weaker O-O bonds.
Q: What happens when sulfur dioxide is dissolved in water?
A: It forms sulfurous acid:

$SO_2 + H_2O → H_2SO_3$

Compounds of Group 16 Elements

Q: Why is hydrogen peroxide ( $H_2O_2$ ) a good oxidizing agent?
A: Due to the presence of an unstable O-O bond that easily breaks to release oxygen.
Q: What happens when sulfur reacts with oxygen?
A: It forms sulfur dioxide:

$S + O_2 → SO_2$

Q: What is the hybridization of sulfur in $SF_6$ ?
A: sp³d²
Q: Why is $H_2S$ a weaker acid than $H_2Te$ ?
A: Because the bond strength decreases down the group, making it easier for $H_2Te$ to donate protons.
Q: Why does $O_3$ act as an oxidizing agent?
A: Due to the easy decomposition of ozone into oxygen and nascent oxygen ( $O_3 → O_2 + O$ ).

Applications & Miscellaneous

Q: Which compound of sulfur is used in vulcanization of rubber?
A: Sulfur ( $S_8$ ).
Q: What is the industrial process for manufacturing sulfuric acid?
A: Contact Process.
Q: Which Group 16 element is used in xerography?
A: Selenium (Se).
Q: Why is polonium highly radioactive?
A: Due to its unstable nucleus, which undergoes radioactive decay.
Q: Why is sulfur dioxide used as a food preservative?
A: It acts as an antimicrobial and antioxidant agent.

25 short question-answer on Group 17 elements

Basic Concepts

Q: Which elements belong to Group 17 of the periodic table?
A: Fluorine (F), Chlorine (Cl), Bromine (Br), Iodine (I), and Astatine (At).
Q: What is the general electronic configuration of Group 17 elements?
A: ns²np⁵
Q: Why are Group 17 elements called halogens?
A: The term "halogen" means "salt-former" because these elements form salts with metals.
Q: Which is the most electronegative element in Group 17?
A: Fluorine (F).
Q: Why does fluorine not show a positive oxidation state?
A: Due to its high electronegativity and the absence of d-orbitals.

Physical Properties

Q: How does atomic size vary down Group 17?
A: It increases from fluorine to astatine due to the addition of electron shells.
Q: Which halogen exists as a liquid at room temperature?
A: Bromine (Br₂).
Q: How does the boiling point of halogens vary down the group?
A: It increases due to stronger van der Waals forces.
Q: What is the physical state of fluorine and chlorine at room temperature?
A: Both are gases.
Q: Why does fluorine have the lowest bond dissociation energy among halogens?
A: Due to strong interelectronic repulsions in the small F₂ molecule.

Chemical Properties

Q: What is the common oxidation state of halogens?
A: -1, but other oxidation states like +1, +3, +5, and +7 are also possible (except for fluorine).
Q: Why is fluorine the strongest oxidizing agent among halogens?
A: Due to its high electronegativity, low bond dissociation energy, and strong hydration energy.
Q: Write the reaction of chlorine with water.
A:

$Cl_2 + H_2O ⇌ HCl + HOCl$

Q: Why is iodine less reactive than chlorine?
A: Due to its larger atomic size and lower bond dissociation energy.
Q: What happens when bromine reacts with ammonia?
A: It forms ammonium bromide:

$3Br_2 + 8NH_3 → 6NH_4Br + N_2$

Compounds of Group 17 Elements

Q: Why is hydrogen fluoride ( $HF$ ) a liquid while hydrogen chloride ( $HCl$ ) is a gas?
A: Due to strong hydrogen bonding in $HF$ .
Q: What is the oxidation state of chlorine in hypochlorous acid ( $HOCl$ )?
A: +1
Q: What happens when chlorine reacts with sodium hydroxide at cold temperatures?
A: It forms sodium hypochlorite ( $NaOCl$ ):

$Cl_2 + 2NaOH → NaCl + NaOCl + H_2O$

Q: What is the hybridization of iodine in $IF_7$ ?
A: sp³d³
Q: Why does fluorine not form $FCl_3$ like chlorine forms $ClF_3$ ?
A: Due to the absence of d-orbitals in fluorine.

Applications & Miscellaneous

Q: Which halogen is used in water purification?
A: Chlorine ( $Cl_2$ ).
Q: Which halogen is essential for thyroid function?
A: Iodine ( $I_2$ ), in the form of iodide ions.
Q: What is the industrial method for preparing chlorine?
A: Electrolysis of brine (Chlor-alkali process).
Q: Which halogen is used in non-stick cookware coatings?
A: Fluorine (in the form of Teflon, $(C_2F_4)_n$ ).
Q: Why is fluorine stored in metal cylinders coated with nickel?
A: Because it reacts with glass and most metals.

25 short question-answer on Group 18 elements

Basic Concepts

Q: Which elements belong to Group 18 of the periodic table?
A: Helium (He), Neon (Ne), Argon (Ar), Krypton (Kr), Xenon (Xe), and Radon (Rn).
Q: What is the general electronic configuration of Group 18 elements?
A: ns²np⁶ (except Helium: 1s²).
Q: Why are Group 18 elements called noble gases?
A: Because they are chemically inert due to their completely filled valence shell.
Q: Which noble gas has the smallest atomic size?
A: Helium (He).
Q: Which noble gas is radioactive?
A: Radon (Rn).

Physical Properties

Q: How does atomic size vary down the Group 18 elements?
A: It increases due to the addition of electron shells.
Q: Why do noble gases have very low boiling points?
A: Due to weak van der Waals forces between atoms.
Q: Which noble gas has the highest ionization energy?
A: Helium (He).
Q: How does density change down the group?
A: It increases from helium to radon.
Q: Why do noble gases have high stability?
A: Because of their completely filled valence orbitals and high ionization energy.

Chemical Properties

Q: Why do noble gases show very low reactivity?
A: Due to their stable electronic configuration and high ionization energy.
Q: Who discovered noble gas compounds?
A: Neil Bartlett in 1962.
Q: Which noble gas forms the most number of compounds?
A: Xenon (Xe).
Q: Write the reaction of xenon with fluorine to form xenon hexafluoride.
A:

$Xe + 3F_2 → XeF_6$

Q: What is the oxidation state of xenon in $XeF_4$ ?
A: +4

Compounds of Noble Gases

Q: Why do krypton and xenon form compounds, but argon does not?
A: Because Kr and Xe have lower ionization energies than argon, making them more reactive.
Q: What is the shape of $XeF_4$ according to VSEPR theory?
A: Square planar.
Q: Name a noble gas compound used in chemical synthesis.
A: Xenon hexafluoroplatinate ( $Xe[PtF_6]$ ).
Q: What is the hybridization of xenon in $XeF_6$ ?
A: sp³d³
Q: Write the hydrolysis reaction of $XeF_4$ .
A:

$XeF_4 + 2H_2O → XeO_2 + 4HF$

Applications & Miscellaneous

Q: Which noble gas is used in filling balloons?
A: Helium (He).
Q: Which noble gas is used in neon signs?
A: Neon (Ne).
Q: Why is argon used in welding?
A: Because it provides an inert atmosphere and prevents oxidation.
Q: Which noble gas is used in cancer treatment?
A: Radon (Rn), in radiation therapy.
Q: Why is xenon used in high-intensity lamps?
A: Due to its ability to produce bright white light.

35 short question-answer on compounds of p block elements

1. Acidic & Basic Strength

Q: Which is more acidic, $H_2O$ or $H_2S$ ?
A: $H_2S$ is more acidic due to weaker H-S bonds compared to H-O bonds.
Q: How does acidic strength vary among hydrides of Group 15?
A: $NH_3 < PH_3 < AsH_3 < SbH_3 < BiH_3$ (Acidic strength increases down the group).
Q: Why is $HF$ a weaker acid than $HCl$ despite fluorine being more electronegative?
A: Due to strong hydrogen bonding in $HF$ , which makes it difficult to dissociate.
Q: Which is more basic, $NH_3$ or $PH_3$ ?
A: $NH_3$ is more basic due to the higher electron density on nitrogen.
Q: How does the basicity of halide ions change in aqueous solution?
A: $I^- < Br^- < Cl^- < F^-$ (F⁻ is the most basic due to its small size and high charge density).
Q: Which is more acidic, $HClO$ or $HClO_4$ ?
A: $HClO_4$ is more acidic due to higher oxidation state and stronger electron-withdrawing effect.
Q: Why is boric acid considered a weak acid?
A: It acts as a Lewis acid by accepting $OH^-$ rather than donating $H^+$ .
Q: How does the acidic nature of oxides of nitrogen vary?
A: $N_2O < NO < N_2O_3 < NO_2 < N_2O_5$ (Acidic nature increases with oxidation state).
Q: Why is $CO_2$ acidic while $SiO_2$ is neutral?
A: $CO_2$ dissolves in water to form carbonic acid, while $SiO_2$ is an acidic oxide but insoluble in water.
Q: Why is $Al(OH)_3$ amphoteric while $NaOH$ is purely basic?
A: $Al(OH)_3$ reacts with both acids and bases, whereas $NaOH$ only reacts with acids.

2. Reducing & Oxidizing Properties

Q: Which is a stronger reducing agent, $H_2S$ or $H_2O$ ?
A: $H_2S$ , because sulfur is less electronegative than oxygen and readily donates electrons.
Q: Why is $HI$ a stronger reducing agent than $HCl$ ?
A: Due to the weaker H-I bond, which makes it easier to donate electrons.
Q: Why is $SO_2$ a reducing agent while $SO_3$ is not?
A: $SO_2$ can be oxidized to $SO_3$ , whereas $SO_3$ is already in its highest oxidation state.
Q: How does reducing strength vary among halides?
A: $F^- < Cl^- < Br^- < I^-$ (Iodide is the strongest reducing agent).
Q: Why does $NH_3$ act as a reducing agent but $NO_2$ acts as an oxidizing agent?
A: $NH_3$ can donate electrons, while $NO_2$ can accept electrons.
Q: Why is $P_4$ more reactive than $N_2$ ?
A: $P_4$ has weaker bonds due to bond strain, while $N_2$ has a strong triple bond.
Q: Why is $ClO_2$ a strong oxidizing agent?
A: Due to the presence of chlorine in a high oxidation state (+4).
Q: Why is $XeF_6$ a strong fluorinating agent?
A: Due to the high oxidizing power of xenon in a high oxidation state.
Q: Why is $HNO_3$ a strong oxidizing agent?
A: Due to the presence of nitrogen in its +5 oxidation state.
Q: Which is a stronger oxidizing agent, $O_2$ or $O_3$ ?
A: $O_3$ (ozone) is stronger due to the release of nascent oxygen.

3. Amphoteric Behavior

Q: Which p-block hydroxide shows amphoteric behavior?
A: $Al(OH)_3$ .
Q: Why is $PbO_2$ amphoteric?
A: It reacts with both acids and bases to form salts.
Q: Why does $ZnO$ exhibit amphoteric nature?
A: It reacts with both $HCl$ (acid) and $NaOH$ (base).
Q: Which oxide is more amphoteric, $Al_2O_3$ or $B_2O_3$ ?
A: $Al_2O_3$ , as $B_2O_3$ is predominantly acidic.
Q: Why is $Sn(OH)_2$ amphoteric?
A: It can react with both acids and bases.

4. Bond Length & Bond Angle

Q: Why is the bond length of $H-F$ shorter than $H-I$ ?
A: Due to the smaller atomic radius of fluorine.
Q: Why is the bond angle in $H_2O$ less than in $NH_3$ ?
A: Due to stronger lone pair repulsions in $H_2O$ .
Q: Why does the bond length of halogens increase down the group?
A: Due to increasing atomic size.
Q: Why is the bond angle in $ClO_2^-$ less than in $NO_2^-$ ?
A: Due to greater lone pair repulsions in $ClO_2^-$ .
Q: Why is the bond length of $NO$ shorter than $NO_2$ ?
A: Due to partial double bond character in $NO$ .

5. Miscellaneous Properties

Q: Why is $H_2O$ liquid while $H_2S$ is a gas?
A: Due to strong hydrogen bonding in water.
Q: Why is $HF$ more viscous than $HCl$ ?
A: Due to extensive hydrogen bonding.
Q: Why is $SiH_4$ less stable than $CH_4$ ?
A: Due to weaker Si-H bonds.
Q: Why does $N_2$ have a triple bond?
A: Due to effective p-p orbital overlap.
Q: Why is $XeF_2$ linear in shape?
A: Due to sp³d hybridization and lone pair repulsions.

25 short question-answer on exceptions in p-block elements

1. Electronic Configuration Exceptions

Q: Why does boron have an incomplete octet in BF₃?
A: Boron has only 6 valence electrons after bonding, making it electron-deficient.
Q: Why does aluminum form AlCl₃ instead of AlCl?
A: Due to the higher stability of Al³⁺ over Al⁺.
Q: Why does nitrogen not form pentahalides like PCl₅?
A: Nitrogen lacks vacant d-orbitals, restricting it to a maximum oxidation state of +3.
Q: Why is the bond angle in NH₃ greater than in PH₃?
A: NH₃ has stronger lone pair-bond pair repulsions due to higher electronegativity of N.
Q: Why is O₂ a paramagnetic molecule despite having an even number of electrons?
A: Due to the presence of unpaired electrons in its antibonding molecular orbitals.

2. Oxidation State Exceptions

Q: Why does fluorine show only a -1 oxidation state while other halogens show multiple oxidation states?
A: Fluorine is the most electronegative element and lacks d-orbitals.
Q: Why does oxygen show a +2 oxidation state in OF₂?
A: Because fluorine is more electronegative, forcing oxygen into a positive oxidation state.
Q: Why does Pb exhibit +2 oxidation state more commonly than +4?
A: Due to the inert pair effect, which stabilizes the lower oxidation state.
Q: Why does Cl exhibit a +7 oxidation state in HClO₄ but not F?
A: Chlorine has vacant d-orbitals, while fluorine lacks them.
Q: Why is +3 oxidation state more stable in Tl (Thallium) than +1?
A: Actually, +1 is more stable due to the inert pair effect.

3. Bonding & Structural Exceptions

Q: Why is B₂H₆ (diborane) an exception in bonding?
A: It has three-center two-electron (3c-2e) bonds instead of normal two-electron bonds.
Q: Why does diamond have a high melting point despite being covalent?
A: Due to its strong 3D network of covalent sp³ bonds.
Q: Why is graphite a good conductor of electricity while diamond is not?
A: Graphite has delocalized π-electrons due to sp² hybridization.
Q: Why does SF₄ have a see-saw shape instead of tetrahedral?
A: Due to the presence of a lone pair on sulfur.
Q: Why does XeF₂ have a linear shape despite sp³d hybridization?
A: Due to the presence of three lone pairs on xenon, which occupy equatorial positions.

4. Acidic & Basic Behavior Exceptions

Q: Why is boric acid considered a Lewis acid despite being a weak acid?
A: It accepts OH⁻ instead of donating H⁺.
Q: Why is HF a weaker acid in water but a stronger acid in non-aqueous solvents?
A: Due to extensive hydrogen bonding in water, reducing its dissociation.
Q: Why does HNO₃ act as both an acid and an oxidizing agent?
A: It donates H⁺ and also contains nitrogen in a high oxidation state (+5), making it an oxidizer.
Q: Why is H₂O liquid while H₂S is a gas?
A: Due to strong hydrogen bonding in water.
Q: Why does SiO₂ behave as an acidic oxide while CO₂ behaves as a gas?
A: SiO₂ forms a strong covalent network, while CO₂ exists as discrete molecules.

5. Reactivity & Stability Exceptions

Q: Why does F₂ have lower bond dissociation energy than Cl₂ despite being smaller?
A: Due to strong lone pair-lone pair repulsions in fluorine.
Q: Why does white phosphorus (P₄) ignite in air while red phosphorus does not?
A: White phosphorus is more reactive due to strain in the P₄ tetrahedral structure.
Q: Why is noble gas xenon able to form compounds while helium and neon do not?
A: Due to lower ionization energy and available d-orbitals in xenon.
Q: Why is H₂O₂ unstable and decomposes easily?
A: Due to weak O-O bond and high tendency to form O₂ and H₂O.
Q: Why does ClF₃ exist but not FCl₃?
A: Because fluorine cannot expand its octet due to the absence of d-orbitals.