According to Einstein, increasing the brightness of a beam of light without changing its color will increase:

Explanation

Einstein proposed the idea that light is quantized into discrete packets of energy called photons. The energy of a photon is directly proportional to its frequency, as given by the equation: [E = hnu] where E is the energy of a photon, h is Planck's constant, and nu is the frequency of the light. When you increase the brightness of a beam of light, you're essentially increasing the total energy being emitted. This can be achieved by increasing the number of photons being emitted, while keeping the color (and thus the frequency) of the light constant. Therefore, option a is correct.