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NDA 2 2025 GAT, question 97

Topic: Chemistry

Q97

Which one of the following statements is NOT correct ?

  1. (a) Water of crystallization is the fixed number of water molecules present in one formula unit of a salt
  2. (b) The molecular formula of Plaster of Paris is CaSO4⋅2H2OCaSO_{4}\cdot 2H_{2}OCorrect answer
  3. (c) Washing soda is used for removing the permanent hardness of water
  4. (d) The atmosphere of Venus is made up of thick white and yellow clouds of sulphuric acid

Solution.

Answer: (b) The molecular formula of Plaster of Paris is CaSO4⋅2H2OCaSO_{4}\cdot 2H_{2}O

  1. Plaster of Paris is calcium sulphate hemihydrate, CaSO4⋅12H2OCaSO_{4}\cdot \frac{1}{2}H_{2}O.
  2. CaSO4⋅2H2OCaSO_{4}\cdot 2H_{2}O is gypsum, so (b) is the statement that is not correct.