State True or False.

If two elements can combine to form more than one compound, the masses of one element that combine with a fixed mass of the other element, are in whole number ratio.

The correct option is A True
When two elements can combine to form more than one compound, the masses of one element that combine with a fixed mass of the other element, are in whole number ratio. This is the law of multiple proportions.
Consider two elements $C$ and $O$. They combine to form $CO$ and $C{O}_2$.
The masses of oxygen that combine with $12$ g of carbon to form $CO$ and $C{O}_2$ are $16$ g and $32$ g respectively. They are in whole number ratio $1:2$.