The correct answer is C. Chlorophyll.
Chlorophyll is a green pigment that is found in the chloroplasts of plants. It is responsible for absorbing sunlight and using that energy to convert carbon dioxide and water into glucose and oxygen. This process is called photosynthesis.
Xanthophyll and carotene are also pigments that are found in plants. However, they do not absorb sunlight as efficiently as chlorophyll. They are responsible for giving plants their yellow, orange, and red colors.
Phaeophytin is a pigment that is found in algae. It is similar to chlorophyll, but it absorbs red light more efficiently. This allows algae to live in deeper water, where there is less sunlight.
In conclusion, chlorophyll is the most important pigment in photosynthesis because it is responsible for absorbing the sunlight that plants need to produce food.