Question

A gas which exists in three allotropic forms $\alpha ,\beta$ and $\gamma$ is :

• A. $S{O}_2$
• B. $S{O}_3$
• C. $C{O}_2$
• D. $N{H}_3$

Answer 1

The correct option is B $S{O}_3$

$S{O}_3$ exists in three allotropic forms.
a) $\alpha -S{O}_3$: It is chemially active form. It forms long transparent ice like crystals. The melting point of this form is ${17}^{o}C$.
b) $\beta -S{O}_3$: It is dimeric ($S_2{O}_6$). It forms needle like silky white crystals. It melts at ${32.5}^{o}C$. Above ${50}^{o}C$, it changes to $\alpha$-form.
c) It is like $\beta$-form and is obtained by completely drying $\beta -S{O}_3$. It melts at ${62.2}^{o}C$ under 2 atmospheric pressure.