Correct Answer - Option 4 : 25

liters
**Given:**

The ratio of petrol to kerosene = 3 : 5

Quantity of solution replaced with petrol = 16 litres

New ratio of petrol to kerosene = 5 : 3

**Calculation:**

Let the initial quantity of petrol and kerosene be 3x and 5x

16 litres of solution replaced with petrol

The solution also in the ratio 3 : 5

so petrol in the replaced solution = (3/8) × 16 = 6 litres

Kerosene in the replaced solution = (5/8) × 16 = 10 litres

According to the question

⇒ (3x - 6 + 16)/(5x - 10) = 5/3

⇒ (3x + 10)/(5x - 10) = 5/3

⇒ 3(3x + 10) = 5(5x - 10)

⇒ 9x + 30 = 25x - 50

⇒16x = 80

⇒ x = 5

The original amount of kerosene = 5x = 25 litres

**∴ The original amount of kerosene in the solution is 25 litres**