The atomic mass of a certain trivalent element is 27. The vapour density of its chloride is 

Atomic weight of trivalent metal, Al = 27 g 
Chloride salt of trivalent metal =$\text{A}\mathrm{l}\text{C}{\mathrm{l}}_3$
$W=27+3(35.5)=133.5g$
$\text{Vapor density,}\left(\text{V.D}\right)=\frac{\text{M.Wt}}{\text{2}}=\frac{133.5}{2}=66.75$