The linear shape of ${\mathrm{C}}_2{\mathrm{H}}_2$  is due to

SP² hybridization of carbon and ${\mathrm{P}}^{\mathrm{\pi }}-{\mathrm{P}}^{\mathrm{\pi }}$  bond.

SP hybridization of carbon and  ${\mathrm{P}}^{\mathrm{\pi }}-{\mathrm{P}}^{\mathrm{\pi }}$ bond.

SP3 hybridization of carbon.

All the above.