Write the structures of all the alkenes which on hydrogenation give $2-$methylbutane.

(N/A) The structure of $2-$methylbutane is $CH_3-CH(CH_3)-CH_2-CH_3$. Hydrogenation of an alkene involves the addition of $H_2$ across the double bond. To obtain $2-$methylbutane,the double bond can be placed between any two adjacent carbon atoms in the skeleton,provided the valency of carbon is maintained.
$(a)$ $CH_3-CH(CH_3)-CH=CH_2$ ($3-$methylbut$-1-$ene)
$(b)$ $CH_3-C(CH_3)=CH-CH_3$ ($2-$methylbut$-2-$ene)
$(c)$ $CH_2=C(CH_3)-CH_2-CH_3$ ($2-$methylbut$-1-$ene)