Concept: The question tests on the area of Rates(Time and Work)

Solution:

Pipe A Takes 2 hours to fill the tank alone.

Work done in 1 hour = 1/2

Let the Leak take x hours to empty the tank.

In 1 hour, work done = 1/x

Pipe A filling and the leak emptying take 2.5 hours to fill the tank.

Work done in 1 hour = 1/2.5 = 2/5


Therefore 1/2−1/x=2/5

1/2−2/5=1/x

5−4/10=1/10=1/x

x = 10 hours

 Option D