Two sources of light emit with a power of $$200$$ W. The ratio of number of photons of visible light emitted by each source having wavelengths $$300$$ nm and $$500$$ nm respectively, will be:

We need to find the ratio of the number of photons emitted by two light sources with the same power but different wavelengths. The energy of a single photon is given by $$E = \frac{hc}{\lambda}$$. If the power of each source is $$P$$, the number of photons emitted per second is $$n = \frac{P}{E} = \frac{P\lambda}{hc}$$, and since both sources have the same power $$P$$, it follows that $$n \propto \lambda$$.

Therefore, the ratio of the number of photons emitted is $$\frac{n_1}{n_2} = \frac{\lambda_1}{\lambda_2} = \frac{300}{500} = \frac{3}{5}$$.

The correct answer is Option (4): 3:5.