p-Block Elements
- Which of the following is incorrect statement ? Answer: 1. PbF ₄ is covalent in nature Go through the statements. PbF₄ is ionic (Pb(IV) with the very electronegative F), so the statement '... 1
- Match the following :(a) Pure nitrogen (i) Chlorine(b) Haber process (ii) Sulphuric acid(c) Contact process (iii) Ammonia(d) Deacon's process (iv) Sodium azide or Barium azideWhich of the following is the correct option ? Answer: 4. (a)-(iv), (b)-(iii), (c)-(ii), (d)-(i) (a) Pure nitrogen: obtained by heating sodium azide or barium azide, (iv). (b) Haber proce... 1
- Which is the correct thermal stability order for H_2E (E = O, S, Se, Te and Po) ? Answer: 3. H ₂ Po < H ₂ Te < H ₂ Se < H ₂ S < H ₂ O Thermal stability of hydrides of group 16 depends on the E-H bond strength, which falls... 1
- The correct structure of tribromooctaoxide is : Answer: 1. (structure 1, see figure) Tribromooctaoxide is the neutral molecule Br₃O₈ with a Br-Br-Br chain. The figure shows the structure w... 1
- Which oxide of nitrogen is not a common pollutant introduced into the atmosphere both due to natural and human activity ? Answer: 1. N ₂ O ₅ N₂O , NO and NO₂ are all released by natural processes (soil bacteria, lightning) and by human activity (fuel combustion,... 1
- Which one of the following elements is unable to form MF_6^3- ion ? Answer: 2. B mathrmMF₆³⁻ needs six F^- around M, so M must use d orbitals to exceed an octet. Boron is in period 2 and has no d orbitals; it... 1
- Which of the following statements is not true for halogens ? Answer: 2. All but fluorine show positive oxidation states. We need the statement that is NOT true for halogens. Option 1: Cl, Br, I and (as... 1
- In which pair of ions both the species contain S-S bond ? Answer: 1. S₄O₆²⁻, S₂O₃²⁻ Key idea: draw the structures. mathrmS₄O₆²⁻ (tetrathionate): has an S-S bond in the chain O₃S-S-S-SO₃ . mathrmS₂O₃... 1
- Match the interhalogen compounds of column I with the geometry in column II and assign the correct code.Column I | Column II(a) XX' | (i) T-shape(b) XX_3' | (ii) Pentagonal bipyramidal(c) XX_5' | (iii) Linear(d) XX_7' | (iv) Square-pyramidal| (v) Tet… Answer: 1. (iii) (i) (iv) (ii) Key idea: use VSEPR for interhalogens. (a) XX': linear (iii) (b) XX₃' : T-shape (i) (3 bond pairs, 2 lone pai... 1
- Which of the following is a sink for CO ? Answer: 1. Micro organisms present in the soil Key idea: CO is removed from air mainly by soil micro-organisms. Certain soil bacteria and fu... 1
- It is because of inability of ns^2 electrons of the valence shell to participate in bonding that : Answer: 4. Sn²⁺ is reducing while Pb⁴⁺ is oxidising Key idea: the inert pair effect makes the +2 state more stable than +4 in heavy group 14... 1
- Name the gas that can readily decolourise acidified KMnO_4 solution : Answer: 1. SO₂ Key idea: KMnO₄ is decolourised by a reducing gas. SO₂ is a reducing agent: 5SO₂ + 2MnO₄^- + 2H₂O → 5SO₄²⁻ + 2Mn²⁺ + 4H^+ . P... 1
- HgCl_2 and I_2 both when dissolved in water containing I^- ions the pair of species formed is : Answer: 2. HgI₄²⁻, I₃^- Key idea: HgI₂ dissolves in excess I^- and I₂ dissolves in I^- by complex formation. HgCl₂ + 2I^-→ HgI₂ (red precipi... 1
- Boric acid is an acid because its molecule Answer: 2. accepts OH^- from water releasing proton Key idea: boric acid is a Lewis acid, not a proton donor. Boron in B(OH)₃ has an empty p... 1
- AlF_3 is soluble in HF only in presence of KF. It is due to the formation of Answer: 1. K₃[AlF₆] Key idea: AlF₃ is covalent and insoluble; extra F^- from KF forms a soluble complex. AlF₃+3KF→ K₃[AlF₆] The stable hexaf... 1
- Which of the following fluoro-compounds is most likely to behave as a Lewis base? Answer: 1. PF₃ Key idea: a Lewis base needs a lone pair to donate. PF₃ : P has a lone pair, so it can act as a donor. CF₄ : no lone pair and... 1
- Hot concentrated sulphuric acid is a moderately strong oxidizing agent. Which of the following reactions does not show oxidizing behaviour? Answer: 3. CaF₂ + H₂SO₄ → CaSO₄ + 2HF Key idea: oxidising behaviour means H₂SO₄ is reduced (S goes from +6 to +4 as SO₂ ). Options 1, 2, 4:... 1
- In context with beryllium, which one of the following statements is incorrect? Answer: 2. Its salts rarely hydrolyze. Key idea: Be is small and highly polarising, so its salts hydrolyse readily. Be forms Be₂C (carbide):... 1
- When copper is heated with conc. HNO_3 it produces : Answer: 1. Cu(NO₃)₂ and NO₂ Key idea: the reduction product of nitric acid depends on its concentration. Cu+4HNO₃(conc.)→ Cu(NO₃)₂+2NO₂+2H₂O... 1
- The product obtained as a result of a reaction of nitrogen with CaC_2 is : Answer: 1. Ca(CN)₂ Key idea: calcium carbide absorbs nitrogen at high temperature to give calcium cyanamide (nitrolim) and carbon. CaC₂+N₂→... 1
- Which is the correct statement for the given acids ? Answer: 2. Phosphinic acid is a monoprotic acid while phosphonic acid is a diprotic acid. Key idea: only the P-OH hydrogens are acidic. Phos... 1
- Which one of the following orders is correct for the bond dissociation enthalpy of halogen molecules ? Answer: 2. Cl₂ > Br₂ > F₂ > I₂ Key idea: bond dissociation enthalpy generally falls down group 17 (bigger atoms, longer bonds), but F₂ is un... 1
- Among the following, the correct order of acidity is : Answer: 2. HClO < HClO₂ < HClO₃ < HClO₄ Key idea: in oxoacids of the same halogen, acidity rises with the number of oxygen atoms (higher oxi... 1