WAEC Chemistry 2015 Paper

Concept:Nitrates of less reactive metals decompose on strong heating to give the free metal, nitrogen dioxide, and oxygen.Explanation:Silver is a less reactive metal. Hence, silver nitrate decomposes on heating to form metallic silver:$$2\mathrm{AgNO_3(s)} \xrightarrow{\Delta} 2\mathrm{Ag(s)} + 2\mathrm{NO_2(g)} + \mathrm{O_2(g)}$$Copper nitrate and lead nitrate are nitrates of moderately reactive metals. They decompose to their metal oxides, not to the free metals.Potassium nitrate, from a very reactive metal, decomposes to potassium nitrite and oxygen.Thus, among the given salts, only silver nitrate produces a metal when heated.Answer:B. $\mathrm{AgNO_3}$