Question 13.21:- 

Write structures of all the alkenes which on hydrogenation give
2-methyl butane.

The basic skeleton of 2-methyl butane is shown below:
C1-CC|2-C3-C4
On the basis of this structure, various alkenes that will give 2-methyl butane on hydrogenation are:
(a) H3C-CHCH3|-CH=CH2     
(b)  CH2=CCH3|-CH-CH3      
(c) CH2=CCH3|-CH-CH3