Which change results in the formation of different substances?
(1) burning of propane
(2) melting of nacl (s)
(3) deposition of co2(g)
(4) solidification of water

In regards to the given question, option “1” is the correct option. When propane is burnt to complete combustion, it results in the formation of two completely different substances. It actually forms a mixture of water vapour and carbon dioxide. When NaCl or sodium chloride is melted, it does not result in the formation of any new substance and so option “2” cannot be the correct answer. With regards to deposition of carbon dioxide and solidification of water, no new substance gets formed and so can be neglected as the answer to the question.

And a) oxygen i believe