Question

A compound is formed when elements X and Y chemically combine with each other. X has a valency of 4 and Y has a valency of 2. The molecular formula of the compound will be _______.

• A. $X_2{Y}_4$
• B. $X_4{Y}_2$
• C. $X_{2}Y$
• D. $X{Y}_2$

Answer 1

The correct option is D $X{Y}_2$

The molecular formula of a compound is derived from the symbols and valancies of its constituting elements using criss cross method, a short-cut method, as shown below.

Symbol: X Y
$\searrow \swarrow$
Valency: 4 2

From the above method, the formula obtained for the compound is $X_2{Y}_4$. This is simplified by taking whole number ratio of the valencies. Thus, molecular formula of the given compound is written as $X{Y}_2$.