Question

Two elements, $X$ and $Y$, have atomic numbers $33$ and $17$, respectively. The molecular formula of a stable compound formed between them is

• A. $XY$
• B. $X{Y}_2$
• C. $X{Y}_3$
• D. $X{Y}_4$

Answer 1

Answer: (C)

$X$ with atomic number $33$ and $Y$ with atomic number $17$ belong to $15th$ and $17th$ group respectively.
Thus, the valency of $X$ and $Y$ are $3$ and $1$ respectively.

$\therefore$ The molecular formula of a stable compound formed between $X$ and $Y$ is $X{Y}_3$.
Here, $X$ could be $As(Z=33)$ and $Y$ could be $Cl(Z=17)$ which gives compound $AsC{l}_3$ .