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 $\lambda_1: \lambda_2$.

A certain orbital having 2 angular nodes and no radial nodes is:

A certain gas absorbs photon of wavelength $4.0 \times 10^{-7} \mathrm{~m}$ and emits radiation at two wavelengths. If one of the emissions occurs at $7.5 \times 10^{-7} \mathrm{~m}$, what is the wavelength at which the second emission occurs?