Final answer:
The frog appears green because of the pigment called chlorophyll a that is present in its cells.
Step-by-step explanation:
The frog appears green because of the pigment called chlorophyll a that is present in its cells. Chlorophyll a absorbs wavelengths from the blue and red ends of the visible spectrum, but not green. Therefore, green light is reflected by the chlorophyll and reaches our eyes, making the frog appear green.