(a) (i) Give reasons for the following: (I) Covalent compounds are poor conductor of electricity. (II) Soap does not form lather in hard water. (III) Carbon shows catenation but silicon does not. (ii) Write chemical equations for the following: (I) Oxidation of ethanol by acidified $\mathrm{K}_2\mathrm{Cr}_2\mathrm{O}_7$ (II) Hydrogenation of ethene. OR (b) Mohan heated ethanol with a compound 'X' in the presence of a few drops of conc. $\mathrm{H}_2\mathrm{SO}_4$ and observed a sweet smelling compound 'Y' is formed. When 'Y' is treated with sodium hydroxide it gives back ethanol and a compound 'Z'. (i) Identify 'X', 'Y' and 'Z'. (ii) Write the role of conc. $\mathrm{H}_2\mathrm{SO}_4$ in the reaction. (iii) Write the chemical equations involved and name the reactions.

(a)(i) These three reasons are directly grounded in Sections 4.1, 4.2 and 4.5 of the NCERT chapter. Covalent bonding involves sharing (not transfer) of electrons, so covalent compounds like carbon compounds form no ions and hence conduct electricity poorly, unlike ionic compounds. Hard water's dissolved $\mathrm{Ca^{2+}}$/$\mathrm{Mg^{2+}}$ salts react with soap to form an insoluble curdy precipitate (scum) as described around Activity 4.11, consuming soap before micelles/lather can form on the remaining dirt. Catenation is unique to carbon (Section 4.2, point (i)) because the strong, stable C–C bond — arising from carbon's small atomic size letting the nucleus hold shared electrons tightly — allows long chains, whereas silicon's larger size gives weak, reactive Si–Si bonds limited to short chains.

(a)(ii) These equations are grounded in Section 4.3.2 (oxidation, where acidified $\mathrm{K_2Cr_2O_7}$/alkaline $\mathrm{KMnO_4}$ oxidise ethanol to ethanoic acid) and Section 4.3.3 (addition/hydrogenation reaction, where unsaturated ethene adds hydrogen over a nickel catalyst to give saturated ethane, exactly as used industrially in hydrogenation of vegetable oils).

(b) This scenario is a direct restatement of Activity 4.8 and Section 4.4.2 (Reactions of ethanoic acid — esterification and saponification) from the chapter. Ethanol + ethanoic acid (X) with conc. $\mathrm{H_2SO_4}$ gives the sweet-smelling ester Y (ethyl ethanoate); treating the ester with NaOH is the saponification reaction that regenerates ethanol and gives the sodium salt Z (sodium ethanoate), matching the chapter's example $\mathrm{CH_3COOC_2H_5 \xrightarrow{NaOH} C_2H_5OH + CH_3COONa}$.