Calculate the relative density of zinc when its density is ${\displaystyle 7g/{cm}^3}$.

Relative density$({\rho }_o)$ is defined as the ratio of the density of any substance to the density of water at ${\displaystyle 4^{\circ }C}$. 

The relative density of water at ${\displaystyle 4^{\circ }C}$ is $1g/c{m}^3$. 

${\mathrm{\rho }}_{\mathrm{o}}=\frac{\mathrm{Density}\mathrm{of}\mathrm{substance}}{\mathrm{Density}\mathrm{of}\mathrm{water}}$

${\rho }_o={\displaystyle \frac{7g/c{m}^3}{1g/c{m}^3}}$

${\rho }_o=7$