The Bohr orbit of the hydrogen atom ( $n=1$ ) is $0.530 \mathop {\rm{A}}\limits^{\rm{o}} $. The radius of the first excited state orbit in $\mathop {\rm{A}}\limits^{\rm{o}} $ is:

The number of electrons with azimuthal quantum numbers $l=1$ and $l=2$ for Cr in the ground state electronic configurations are respectively. [Given: $\mathrm{Cr}(\mathrm{Z}=24)$ ]

The ratio of the difference between the radii of $3^{\text {rd }}$ and $4^{\text {th }}$ orbits of the $\mathrm{He}^{+}$and those of $\mathrm{Li}^{2+}$ is:

Two subatomic particles 1 and 2, with the same kinetic energies have their de- Broglie wavelengths as $\lambda_1 \& \lambda_2$ and masses as 3 m and 6 m respectively. Determine the ratio $\lambda_1: \lambda_2$.