Which example is most suitable for the law of gaseous volumes?

Correct answer: Volume ratios of gases at same temperature pressure

The direct answer is option A: volume ratios of gases measured at the same temperature and pressure. The law of gaseous volumes concerns the volumes of reacting gases and gaseous products, not unrelated physical properties. To solve this, first look for the word gas; next look for volume or volume ratio; finally check that the measurements use common temperature and pressure. Option A contains all three essential ideas, so it is the best example. Option B, the melting point of a solid, is a property of a solid and gives no reacting-gas volume ratio. Option C, the amount of sand in a mixture, concerns a mixture and not gaseous reaction volumes. Option D, the lustre of a metal, is an appearance property and is unrelated to this law. The law does not say that all physical properties have fixed values; it specifically describes simple volume relationships in gas reactions under comparable conditions. Therefore A is correct. Exam reminder: gas volume plus same temperature and pressure is the identifying pattern for Gay-Lussac's law.