Question

Sol. Key concept: Identify ionic interactions and covalent/coordinate bonding in the conventional school model.

NH₄Cl contains ionic attraction between NH₄⁺ and Cl⁻. The N–H bonds are covalent, and formation of NH₄⁺ from NH₃ and H⁺ is described as donation of a nitrogen lone pair to the proton.

KNO₃ has ionic attraction between K⁺ and NO₃⁻ and covalent N–O bonding within nitrate. Traditional school Lewis structures represent one N–O contribution as a coordinate bond.

CuSO₄·5H₂O has ionic constituents, covalent bonds within sulfate/water, and coordinate bonding from water-oxygen lone pairs to Cu²⁺. HNO₃, by contrast, is molecular and does not itself supply the ionic solid bonding required in set (b). Thus (c) is the intended answer.

Correction / clarification: Once formed, a coordinate bond is a covalent bond; the N–H bonds in NH₄⁺ are equivalent, and nitrate bonding is delocalised. The arrows in a Lewis structure describe electron-pair bookkeeping, not a permanently distinct physical bond.