The maximum number of orbitals which can be identified with $$\mathrm{n}=4$$ and $$m_l=0$$ is _________.

The de-Broglie's wavelength of an electron in the $$4^{\text {th }}$$ orbit is ________ $$\pi \mathrm{a}_0$$. ($$\mathrm{a}_0=$$ Bohr's radius)

The ionization energy of sodium in $$\mathrm{~kJ} \mathrm{~mol}^{-1}$$, if electromagnetic radiation of wavelength $$242 \mathrm{~nm}$$ is just sufficient to ionize sodium atom is _______.

Number of spectral lines obtained in $$\mathrm{He}^{+}$$ spectra, when an electron makes transition from fifth excited state to first excited state will be