(i) Write three characteristic properties of nuclear force.

(ii) Draw a plot of potential energy of a pair of nucleons as a function of their separation. 

OR

Determine the wavelength of the radiation required to excite the electron in Li⁺⁺ from the first to the third Bohr orbit.  

(i) Characteristics properties of nuclear force

(a) Nuclear forces act between a pair of neutrons, a pair of protons and also between a neutron-proton pair, with the same strength. This, shows that, nuclear forces are independent of charge.

(b) The nuclear forces are dependent on spin or angular momentum of nuclei.

(c) Nuclear forces are non-central forces. This shows that, the distribution of nucleons in a nucleus is not spherically symmetric.

(ii)

OR

Given, for Li+ +, Z = 3 and as the excitation is from first to

third Bohr orbit, so n₁ = 1, n₂ = 3.

Using the relation,

$\frac{1}{\mathrm{\lambda }}={\mathrm{Z}}^2\mathrm{R}\left(\frac{1}{{\mathrm{n}}_1^2}-\frac{1}{{\mathrm{n}}_2^2}\right)={\left(3\right)}^2\mathrm{R}\left(\frac{1}{1}\right)$