Science (086) — AI-generated practice question

(i) Covalent compounds have low melting and boiling points because, although the covalent bonds within molecules are strong, the intermolecular forces between molecules are very weak. Very little energy is needed to overcome these weak forces.

(ii) Unsaturated hydrocarbons have a high proportion of carbon relative to hydrogen. They undergo incomplete combustion due to insufficient oxygen, releasing fine carbon particles (soot) that glow yellow, producing a sooty yellow flame.

(iii) Methanol is far more dangerous because even a small quantity can cause death. In the liver, methanol is oxidised to methanal (formaldehyde), which coagulates the protoplasm of cells and damages the optic nerve, causing permanent blindness or death.

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• For (i), the key phrase from the textbook is: "covalently bonded molecules have strong bonds within the molecule, but intermolecular forces are weak" — always mention both aspects.
• For (ii), the sooty flame question tests understanding of C:H ratio and incomplete combustion — link high carbon content → insufficient oxygen → soot.
• For (iii), quote the specific biochemical effect (methanal, protoplasm coagulation, optic nerve damage) — these are the scoring points examiners look for.