# 0.14 g of an element on combustion gives 0.28 g of its oxide. What is that element ?

$\begin {array} {1 1} (1)\;Nitrogen & \quad (2)\;Carbon \\ (3)\;Fluorine & \quad (4)\;Sulphur \end {array}$

You can see that the mass of added oxygen must be 0.14 g, the same as the sulphur. Of all  the choices available, only in SO2 would the mass of oxygen be the same as that of the sulphur. Sulphur's atomic weight = 32 and two oxygen atoms would add up to 32 as well.
edited Dec 24, 2014 by pady_1