Question

mercuric oxide on heating gives mercury n oxygen - give reason

Answer 1

Mercury(II) oxide, a red solid, decomposes when heated to produce mercury and oxygengas. A reaction is also considered to be a decomposition reaction even when one or more of the products are still compounds. A metal carbonate decomposes into a metal oxide and carbon dioxide gas.

Answer 2

The heat energy is enough to break the bonds of Mercury and Oxygen and hence it decomposes into Mercury metal and Oxygen gas.

This is also an example of thermal decomposition.