Answer
See explanation.
Work Step by Step
a. The frequency is $f=\frac{c}{\lambda}=5.00\times10^{14}Hz $.
b. Find the energy of one photon.
$$ E=hf=h\frac{c}{\lambda}$$
$$E=\frac{1.24\times10^{-6}eV\cdot m}{600\times10^{-9}m}=2.07 eV=3.31\times10^{-19}J$$
The number of photons emitted per second is $\frac{75J}{3.31\times10^{-19}J }=2.3\times10^{20}$
c. No. The frequency of the light depends on the color of the light. The number of photons emitted per second depends on the power output by the source.
