Question

An element X forms a compound XH₃ with hydrogen. Another element Y forms a compound YX₂ with X. Given that the valency of hydrogen is 1, what are the valencies of X and Y?

Answer 1

Let the valency of X in XH₃ is x.

Valency of H = 1 (Given)

As, NH₃ is a neutral molecule, so,

$$\begin{gathered} (\mathrm{Valency}\mathrm{of}\mathrm{X})+(3\times \mathrm{Valency}\mathrm{of}\mathrm{H})=0 \\ \Rightarrow \left(\mathrm{x}\right)+(3\times 1)=0 \\ \Rightarrow \mathrm{x}=-3 \end{gathered}$$

So, the valency of X is $-$3.

Let's assume the valency of Y in YX₂ = y

Valency of X = $-$3

As, YX₂ is a neutral molecule, so,

$$\begin{gathered} (\mathrm{Valency}\mathrm{of}\mathrm{Y})+(2\times \mathrm{valency}\mathrm{of}\mathrm{X})=0 \\ \Rightarrow \left(\mathrm{y}\right)+(2\times (-3\left)\right)=0 \\ \Rightarrow \mathrm{y}=6 \end{gathered}$$

So, the valency of Y in YX₂ is 6.

Hence, the valency of X is $-$3 and valency of Y is 6.