Q4. PbF4 and PbCl4 are known, but PbBr4 and PbI4 are unstable. Explain.
Lead(IV) is an oxidising agent, because lead is more stable as +2 (the inert pair effect). Bromide and iodide ions are easily oxidised, so they reduce Pb(IV) to Pb(II), and the tetrabromide and tetraiodide break down. Stability: PbF4 > PbCl4 > PbBr4 > PbI4 (Wikipedia, “Lead” and “Carbon group”; reasoned).
Q5. What mass of chlorine does 23.92 g of PbO2 give with excess hydrochloric acid? (Pb = 207.2, O = 16.00, Cl = 35.45 g mol−1.)
M(PbO2) = 207.2 + 32.00 = 239.2 g mol−1, so 23.92 g is 0.1000 mol. PbO2 + 4HCl → PbCl2 + Cl2 + 2H2O gives 0.1000 mol Cl2, which is 0.1000 × 70.90 = 7.09 g (reasoned from NCERT Class 11 Chemistry, page 246).
Q6. Assertion: SiCl4 is hydrolysed by water but CCl4 is not. Reason: silicon can accept a lone pair from water into its vacant 3d orbitals. Are both true, and does the reason explain the assertion?
Both are true, and on NCERT’s account the reason explains the assertion: silicon, with nine valence orbitals including 3d, can expand its valence shell and accept a lone pair from water, while carbon, with only 2s and 2p, cannot (reasoned from NCERT Class 11 Chemistry, page 93). Give that answer in an exam. Beyond the NCERT text: modern bonding analyses find little d-orbital participation (Reed and Schleyer, JACS, 1990; Wikipedia, “Hypervalent molecule”). SiCl4 reacts in two steps through a five-coordinate silicon intermediate, while CCl4 could react only in one step with a very large activation energy, so it is stable in water (International Chemistry Olympiad 2021, preparatory problem 14).
Q7. Name the metalloids of group 14, and the form of tin that appears below 13.2 °C.
Silicon and germanium are the metalloids. Below 13.2 °C silvery β-tin slowly turns into grey, powdery α-tin (Wikipedia, “Carbon group”).
Q8. Why does carbon show catenation far more than silicon?
Catenation depends mainly on the strength of the bond between two atoms of the element. Carbon’s compact 2p orbitals overlap strongly, so C–C bonds are strong and long chains are stable; the larger, more diffuse orbitals of silicon give weaker Si–Si bonds (Wikipedia, “Catenation”).