Question

Gold ornaments do not change their appearance on exposure to air whereas silver ornaments turn black after sometime . give reason

Answer 1

because gold is mixed with copper to make gold ornaments
silver is not mixed with anything

Answer 2

Silver turns black or tarnishes due to a chemical reaction caused by the contact of sulphor or hydrogen.Even polluted air can turn sterling silver into black.It gets blackened or 'tarnished' - a sulphur reaction in the metal.

-Hope this helps :))