Find the energy released when two ${}_1{\mathrm{H}}^2$ nuclei fuse together to form a single ${}_2{\mathrm{He}}^4$ nucleus. Given, the binding energy per nucleon of ${}_1{\mathrm{H}}^2$ and ${}_2{\mathrm{He}}^4$ are $1.1 \mathrm{MeV}$ and $7.0 \mathrm{MeV}$ respectively.

State the postulates of Bohr atom model. Obtain the expression for the radius of the ${\mathrm{n}}^{\mathrm{th}}$ orbit of an electron based of Bohr's theory.

The distance of the closest approach of an $\mathrm{\alpha }-$particle reaching a nucleus with momentum $\text{'}\mathrm{p}\text{'}$ is ${\mathrm{r}}_0$. When the $\mathrm{\alpha }-$ particle travels towards the same nucleus with momentum $\frac{\mathrm{P}}{2}$, the distance of the closest approach will be:

When a hydrogen atom absorbs an energy of $10.2 \mathrm{eV}$, the change in its angular momentum is:

Define curie.

Half lives of two radioactive elements are $12$ hrs and $16$ hrs respectively. If at any instant, the ratio of the amounts of radioactive substances is $2:1$, then after $2$ days, what will be the ratio of the undecayed portions?

Explain the spectral series of hydrogen atom. (Diagram not necessary)

Explain the construction and working of a Geiger-Muller counter.