The difference between excitation energy and binding energy of electron in a He+ ion is 42.31 eV. The energy quantum number of the excited state is

E0=Energy of electron in the ground state =−13.6Z2 eVE = Energy in excited state =-13.6Z2n2eVBinding energy in the excited state =+13.6Z2n2eVExcitation energy =−13.6Z2n2−(−13.6Z2)eV=13.6Z2(1−1n2)eV∴ Difference =13.6Z2(1−1n2)−13.6Z2n2=13.6Z2(1−2n2)eV∴13.6×22×(1−2n2)=42.31⇒n=3