Step 1: Recall what ozonolysis does to a double bond.
Reductive ozonolysis cleaves the C=C bond and turns each carbon into a carbonyl carbon, so working backwards, each product's carbonyl oxygen is replaced by a double bond back to its partner fragment.
Step 2: Look at the two fragments.
Ethanal gives the fragment $\text{CH}_3-\text{CH}=$, and pentan-3-one gives the fragment $=\text{C}(\text{C}_2\text{H}_5)_2$, since pentan-3-one's carbonyl carbon carries two ethyl groups.
Step 3: Rejoin the two fragments with a double bond.
\[ \text{CH}_3-\text{CH}=\text{C}(\text{C}_2\text{H}_5)_2 \]
Step 4: Number the longest chain through the double bond.
Choosing the five-carbon chain that includes both double-bond carbons gives pent-2-ene as the parent, with one ethyl branch left over on C3.
Final answer: Option 3, 3-Ethylpent-2-ene.