A double charged lithium atom is equivalent to hydrogen whose atomic number is 3. The wavelength of required radiation for emitting electron from first to third Bohr orbit in Li++ will be (Ionisation energy of hydrogen atom is 13.6eV) 
(a) 182.51 Å                 (b) 177.17 Å
(c) 142.25 Å                 (d) 113.74 Å

(d) En=-13.6Z2n2 eV Required energy for said transition

E=E3-E1=13.6 Z2112-132

E=13.6×3289=108.8 eV

E=108.8×1.6×10-19 J

Now E=hcλ=108.8×1.6×10-19

λ=6.6×10-34×3×108108.8×1.6×10-19=0.11374×10-7 m= 113.74 A0

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