Question

gold ornaments do not change their appearance on exposure to air where silver ornaments appear black after some time. what could be reason for this change?

Answer 1

turns black in colour after it is exposed to air because of sulphur present in the year when silver reacts with Sulphur it forms silver sulphide which is black in colour

Answer 2

...Silver should turn black when exposed to air.  This is because it reacts with air to form  Silver sulfide or Silver oxide.  To prevent this, you could rub toothpaste or baking soda.