A photon of 400 nm is absorbed by a gas molecule and then the molecule re-emits two photons. One re- — Atomic Structure Chemistry Question

💡 Solution & Explanation

Energy conservation: $E_{\text{in}} = E_{\text{out1}} + E_{\text{out2}} \implies \frac{hc}{\lambda_{\text{in}}} = \frac{hc}{\lambda_1} + \frac{hc}{\lambda_2} \implies \frac{1}{400} = \frac{1}{500} + \frac{1}{\lambda_2} \implies \frac{1}{\lambda_2} = \frac{1}{400} - \frac{1}{500} = \frac{5-4}{2000} = \frac{1}{2000}$. Thus $\lambda_2 = 2000$ nm. Therefore, correct answer is B.