According to the question, the pump takes 2.5 hours to fill the tank because of the leakage.

Normally with no leakage it takes 2 hours to fill the tank. We can say that 25% of the tank will be filled in 0.5 hours.

There is difference of 0.5 hours between filling and leaking. And the leak empties 25% of the tank in 2.5 hours

so, 100% of the tank will be empties in $\frac{100}{25}\times 2.5=4\times 2.5=10 \mathrm{hours}$

Hence option A is correct