1. Identify the reaction

Ethanal is an aldehyde with formula: $\text{CH}_3\text{CHO}$

Semicarbazide has the structure: $\text{NH}_2\text{-NH-CO-NH}_2$

Aldehydes react with semicarbazide to form semicarbazones.

2. Write the reaction

The carbonyl group of ethanal reacts with semicarbazide with loss of one molecule of water: $\text{CH}_3\text{CHO} + \text{H}_2\text{N-NH-CO-NH}_2 \rightarrow \text{CH}_3\text{CH=N-NH-CO-NH}_2 + \text{H}_2\text{O}$

3. Count the nitrogen atoms in the product

The product is ethanal semicarbazone: $\text{CH}_3\text{CH=N-NH-CO-NH}_2$

Nitrogen atoms present are:

• one in $\text{CH=N}$
• one in $\text{-NH-}$
• one in $\text{-NH}_2$

So total number of nitrogen atoms $= 3$.

4. Final answer

The compound formed contains: $\boxed{3}$

5. Comparison with stored answer

Stored correct answer = $3$

My derived answer = $3$

Hence, they agree.