An $\alpha$-particle of energy $4\  MeV$ is scattered through $180^o $ by a fixed uranium nucleus. The distance of the closest approach is of the order of

Energy levels $A, B, C$ of a certain atom correspond to increasing values of energy i.e., $E_A < E_B < E_C$. If ${\lambda _1},{\lambda _2},{\lambda _3}$ are the wavelengths of radiation corresponding to the transition $C$ to $B, B$ to $A$ and $C$ to $A$ respectively, which of the following relation is correct ?

A $10\; kg$ satellite circles earth once every $2 \;hours$ in an orbit having a radius of $8000\; km$. Assuming that Bohr's angular momentum postulate applies to satellites just as it does to an electron in the hydrogen atom, find the quantum number of the orbit of the satellite.

The wavelength of ${K_\alpha }$ line for an element of atomic number $29$ is $\lambda $ . Then the wavelength of ${K_\alpha }$ line for an element of atomic no $15$ is (Take mosley‘s constant $b = 1$ for both elements)

If in nature there may not be an element for which the principal quantum number $n > 4,$ then the total possible number of elements will be

The number of completely filled shells for the element ${ }_{16} S ^{32}$ is