JEE Main · 2021 · 27 Aug 2021 · Shift 1 · s-Block Elements

The number of water molecules in gypsum, dead burnt plaster and plaster of paris, respectively are:

Answer: (C)

Solution

Gypsum is

CaS O_{4} \cdot 2 H_{2} O

and holds two water molecules per formula unit. Dead burnt plaster is anhydrous

CaS O_{4}

and holds none. Plaster of Paris is

CaS O_{4} \cdot \frac{1}{2} H_{2} O

and holds half a water molecule per formula unit. The numbers are therefore

2

0

and

0.5

respectively.

JEE Main · 2021 · 27 Aug 2021 · Shift 1 · Single correct option