Q-If each hydrogen atom is excited by giving 8.4 eV of energy then the number of spectral lines emitted is equal to:
(A) None (B) Two (C) Three (D) Four

Isolated hydrogen atom can absorb any of the following quanta of energy, given by the equation

Energy absorbed =13.6 ( 1 - ( 1 / n² ) e.v. ; where n can take whole number values  from 1 to infinity.

For any value of 'n' it cannot be 8.4 e.v.

So, hydrogen atom out rightly rejects that quantum. No electronic excitation takes place- no emission of radiation and it will not result in any spectral line. So, answer is 'none'

a) none

as min of 10.2 eV of energy is required to make the electron get excited.