Nuclear fission of heavy nuclei and fusion of light nuclei both release energy because the binding energy per nucleon of the products exceeds that of the reactants.

A mass defect of 0.01 amu corresponds to approximately $x$ MeV. Nearest integer $x$:

The energy equivalent of 1 amu is approximately:

Binding energy per nucleon is maximum for nuclei around:

The energy source of the sun is primarily:

The half-life of a radioactive sample is $T$. After time $3T$, the fraction remaining is: