0.2429 g sample of potassium is heated in oxygen 0.440 g of a crystalline compound is obtained. What is the formula of this compound?

Mass of K= 0.242 g, rmss of compound = 0.440 g ,

mass of O = 0.440-0.242  = 0.198 g

$\text{ Relative molar ratio of }\mathrm{K}=\frac{0.242}{39}=0.0006\text{, }$

$\text{ Relative molar ratio of }\mathrm{O}=\frac{0.198}{16}=0.012$

Simple ratio of K = 1

Simple ratio of O = 2

So, the formula is ${\mathrm{KO}}_2$.