100g of mercuric oxide decompose to give 92.6g of mercury and 7.4g of oxygen and 10g of oxygen react completely with 125g of mercury to give mercuric oxide. These points will follow

The synthesis of elements or compounds from their constituents should be follow the law constant proportions.

The chemical equations for decomposition and combination reaction are given below.

$100\text{gm}\text{of}\text{HgO}\to 92.6\text{g}\text{of}\text{Hg}+7.4\text{g}\text{of}\text{oxygen}$

$x\text{gm}\text{of}\text{HgO}\to \text{125g}\text{of}\text{Hg }+10\text{gm}\text{of}\text{oxygen}$

$\Rightarrow x=135\text{gm}\text{of HgO}$

(i.e) 100 gm of HgO contains 7.4 g of oxygen

135 g of HgO contains 10 g of oxygen.