Which of the following alkenes on ozonolysis give a mixture give a mixture of ketons only?

1.  ${\mathrm{CH}}_{3}-\mathrm{CH}=\mathrm{CH}-{\mathrm{CH}}_{3}$

2.

3.

4.

(3, 4)
Alkenes which have two substituents on each carbon atom of the double bond, give mixture of ketones on ozonolysis. Thus, option (3) and (4) give mixture of ketones.
3.
4.
On the other hand, alkenes (a) and (b) give a mixture of two aldehydes.
1.
2.