Find the total number of species having linear shape.

${\mathrm{C}}_2{\mathrm{H}}_2,{\mathrm{CO}}_2,{\mathrm{SnCl}}_2,{\mathrm{HgCl}}_2,\mathrm{HCN},{\mathrm{O}}_3,{\mathrm{OF}}_2,{\mathrm{XeF}}_2$

The species having linear shape is ${\mathrm{C}}_2{\mathrm{H}}_2,{\mathrm{CO}}_2,{\mathrm{HgCl}}_2,\mathrm{HCN},{\mathrm{XeF}}_2$.

Because every atom in ${\mathrm{C}}_2{\mathrm{H}}_2,{\mathrm{CO}}_2,{\mathrm{HgCl}}_2,\mathrm{HCN},{\mathrm{XeF}}_2$ is symmetrically placed in the same plane, the compound has a linear molecular structure. Due to their lower electronegative nature than Hydrogen atoms, both Carbon atoms are located in the center of the Lewis structure of C2H2.

Hence, the total number of species having linear shape is 5.