What is the radius of the fourth orbit of $Be^{3+}$ (in $pm$)?

Which formula is used to calculate the energy of a species containing $1$ electron?

When $\alpha$-particles are sent through a thin metal foil,most of them go straight through the foil because (one or more are correct)

Typical electronic energy gaps in molecules are about $1.0 \ eV$. In terms of temperature,the gap is closest to

The value of Planck's constant is $6.63 \times 10^{-34} \, J \cdot s$ and the speed of light is $3.0 \times 10^8 \, m \cdot s^{-1}$. The wavelength of a quantum of light with a frequency of $8 \times 10^{15} \, s^{-1}$ is closest to which of the following values in meters?

Which of the following transitions emits a photon with the maximum frequency?