The mass defect in a particular nuclear reaction is 0.3 grams. The amount of energy liberated in kilowatt hours is (Velocity of light = 3 × 10⁸ m/s)

7.5 × 10⁶ 

$E=\Delta m . c^2 \Rightarrow E=\frac{0.3}{1000} \times\left(3 \times 10^8\right)^2=2.7 \times 10^{13}$ J

= $\frac{2.7 \times 10^{13}}{3.6 \times 10^6}=7.5 \times 10^6$ kWh.