The number of isomers of dibromoderivative (molar mass $186 \mathrm{g} {\mathrm{mol}}^{-1}$) of an akene is

Alkenes are known to have at least one double bond. It will have 160 moles if we take 2 bromine atoms. 

The three isomers are ${\mathrm{Br}}_2\mathrm{C}={\mathrm{CH}}_2$ and cis- and trans-isomers of $\mathrm{BrCH}=\mathrm{CHBr}.$

Weight-wise, the only elements left are 2C and 2H, with 2Br atoms put at either one carbon atom or both carbon atoms, depending on your preference. that will result in geometric isomerism (2-Forms).