Name the pigment which occurs in all photosynthetic protists.

Explanation

To answer the question about the pigment that occurs in all photosynthetic protists, we can follow these steps:

### Step-by-Step Solution:

1. **Identify Photosynthetic Protists**: Recognize that photosynthetic protists include various groups such as red algae, green algae, brown algae, diatoms, and dinoflagellates.

2. **Examine Pigments in Red Algae**: Red algae contain chlorophyll A, carotenoids, and phycobilins.

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