As per the given information, propanal and pentan-3-one are the ozonolysis products of an alkene. Let the given alkene be ‘A’. Writing the reverse of the ozonolysis reaction, we
get: 

   $H_{3}C-C{H}_2-CHO+C{H}_2-\underset{\underset{O}{\parallel }}{C}-C{H}_2-C{H}_3$
$Propanal\uparrow Zn+H_{2}O Pen\tan t-3-one$
$\text{'}X\text{'}$
$Ozonide$
$\uparrow$
$\text{'}A\text{'}+O_3$
$Alkene$
$$

 The products are obtained on the cleavage of ozonide ‘X’. Hence, ‘X’ contains both products in the cyclic form. The possible structure of ozonide can be represented as:

Now, ‘X’ is an addition product of alkene ‘A’ with ozone. Therefore, the possible structure of alkene ‘A’ is:

$H_{3}C-C{H}_2-CH=C-C{H}_2-C{H}_3$
$|$
$C{H}_{2}C{H}_3$