If the frequency required for the transition from 2nd to 5th orbit is 4 x \( { 10}^{ 15} \) Hz, what will the corresponding energy be?

16.5 eV

The correct answer is option 2: 16.5 eV

energy : E = hv

v = 4 x \( { 10}^{ 15} \) Hz

$ E = 6.63\times 10^{-34}\times 4\times 10^{15} J = 16.5 eV$

While multiplying h and ν gives a number around 2.65, that is in joules, not eV. Therefore, the correct energy in electron volts is approximately 16.5 eV.