Determine the empirical formula of an oxide of iron which has $69.9 \%$ iron and $30.1 \%$ dioxygen by mass.

An organic compound has the percentage of $C$ and $H$ in the ratio $6 : 1$ and the percentage of $C$ and $O$ in the ratio $3 : 4$. The compound is:

An oxide of copper which is red in colour has the formula

$0.44 \ g$ of a colourless oxide of nitrogen occupies $224 \ mL$ at $\text{STP}.$ The compound is $-$

If we want to study the relative arrangement of atoms in a molecule,we study:

Compound $A$ contains $8.7\,\%$ Hydrogen,$74\,\%$ Carbon and $17.3\,\%$ Nitrogen. The molecular formula of the compound is ....
Given : Atomic masses of $C$,$H$ and $N$ are $12$,$1$ and $14\, amu$ respectively.
The molar mass of the compound $A$ is $162\, g\, mol^{-1}$.