Question

Suppose that a maximum of 25 g of salt dissolves in 100 g of water. Any more salt, if added, remains undissolved and a sediment falls at the bottom. Now, water is evaporated from 1 kg of a 4% solution at the rate of 28 g per hour. After how long will it start sedimenting, approximately?

• A. 29 h
• B. 31 h
• C. 35 h
• D. 23 h

Answer 1

Answer: (B)

31 h

Answer 2

25 gm salt in 100 gm water

1 gm $=\frac{100}{25}$

40 gm $=\frac{100}{25}\times40=160$ gm

Water is evaporated at 28 gms per hour
From option C, we get
after 30 hrs
water loss = 30$\times$28
= 840
Present value of water = 1000 - 840 = 160 gms
After 30 hrs, water will start to reduce and salt will begin to sediment.
So the correct option is (B)