Energy released when two deuterons $\left({ }_1 H ^2\right)$ fuse to form a helium nucleus $\left({ }_2 He ^4\right)$ is $:$
(Given $:$ Binding energy per nucleon of ${ }_1 H ^2=1.1 \ \text{MeV}$ and binding energy per nucleon of ${ }_2 He ^4=7.0 \ \text{MeV}$) (in $\text{MeV}$)

Assertion: Heavy water is a better moderator than normal water.
Reason: Heavy water absorbs neutrons more efficiently than normal water.

$A$ star has $10^{40}$ deuterons. It produces energy via the processes:
$_1H^2 + _1H^2 \to _1H^3 + p$
$_1H^2 + _1H^3 \to _2He^4 + n$
If the average power radiated by the star is $10^{16} \ W$, the deuteron supply of the star is exhausted in a time of the order of:
Given:
Mass of $_1H^2 = 2.014 \ amu$
Mass of $_2He^4 = 4.001 \ amu$
Mass of proton = $1.007 \ amu$
Mass of neutron = $1.008 \ amu$

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