The spectrum of helium is similar to which of the following?

The $\alpha$-particle scattering experiment of Rutherford concluded that

If the electron jumps from $7.00 \ eV$ energy level to $5.0 \ eV$ energy level,it :

Number of waves made by Bohr's electron in one complete revolution in the $3^{rd}$ orbit.

Energy of an electron in the ground state of the hydrogen atom is $-2.18 \times 10^{-18} \ J$. Calculate the ionization enthalpy of atomic hydrogen in terms of $J \ mol^{-1}$.

The wavelength of a particle having an Einstein energy of $1.995 \times 10^{12} \ erg \ mol^{-1} \ photon^{-1}$ is .......... $\mathring{A}$.