Consider a helium (He) atom that absorbs a photon of wavelength 330 nm. The change in the velocity (in cm s^$$-$$1) of He atom after the photon absorption is __________.

(Assume : Momentum is conserved when photon is absorbed.

Use : Planck constant = 6.6 $$\times$$ 10^$$-$$34 J s, Avogadro number = 6 $$\times$$ 10²³ mol^$$-$$1, Molar mass of He = 4 g mol^$$-$$1)

The figure below is the plot of potential energy versus internuclear distance (d) of H₂ molecule in the electronic ground state. What is the value of the net potential energy E₀ (as indicated in the figure) in kJ mol^-1, for d = d₀ at which the electron-electron repulsion and the nucleus-nucleus repulsion energies are absent? As reference, the potential energy of H atom is taken as zero when its electron and the nucleus are infinitely far apart.
Use Avogadro constant as 6.023 $$ \times $$ 10²³ mol^-1.

Not considering the electronic spin, the degeneracy of the second excited state( n = 3) of H atom is 9, while the degeneracy of the second excited state of H^– is ___________.

In an atom, the total number of electrons having quantum numbers n = 4, |m_l| = 1 and m_s = –1/2 is