The equivalent mass of chlorine is 35.5 and the atomic mass of copper is 63.5. The equivalent mass of copper chloride is 99.0. Hence, formula of copper chloride is 

Equivalent mass of copper chloride = 99

Equivalent mass of chlorine =35.5 

$\therefore$ Equivalent mass of copper =99-35.5 = 63.5

$\therefore \text{ Valency of copper }=\frac{\text{ Atomic mass of copper }}{\text{ Equivalent mass of copper }}=1$

$\therefore$Formula of copper chloride is CuCl.