Among the following allotropic form of sulphur, the number of allotropic forms, which will show paramagnetism is

a) $\alpha$-sulphur

b) $\beta$-sulphur

c) ${\mathrm{S}}_2$-form

The paramagnetic behaviour of compound is shown when it is being placed in external magnetic field. Due to presence of unpaired electron, the molecule will show paramagnetic behaviour and also known as paramagnetism.

The ${\mathrm{S}}_2$-form of sulphur will only show paramagnetism.

Hence, the number of allotropic forms, which will show paramagnetism is $1$.