Consider the following compounds : FeSO₄ ; CuSO₄ ; CaSO₄ ; Na₂CO₃ The compound having maximum number of water…

Question

Consider the following compounds :
FeSO₄ ; CuSO₄ ; CaSO₄ ; Na₂CO₃
The compound having maximum number of water of crystallisation in its crystalline form in one molecule is :

Accepted Answer

## Model Answer **(d) Na₂CO₃** Na₂CO₃·10H₂O (washing soda) has **10 water molecules** of crystallisation, which is the maximum among the given compounds (FeSO₄·7H₂O, CuSO₄·5H₂O, CaSO₄·2H₂O). Source: Chapter 2, Section 2.4.4 --- ## Explanation The water of crystallisation for each compound: - FeSO₄·7H₂O → 7 molecules - CuSO₄·5H₂O → 5 molecules - CaSO₄·2H₂O → 2 molecules - **Na₂CO₃·10H₂O → 10 molecules** ✓ The textbook explicitly states Na₂CO₃·10H₂O (washing soda). Note: FeSO₄·7H₂O is not mentioned in the passage but is standard NCERT knowledge; Na₂CO₃ with 10 water molecules is the clear winner. Always remember the formula of washing soda for board exams.

Science — CBSE Class 10 board question