Explanation:

An autotroph is an organism that can produce its own food through photosynthesis or chemosynthesis. Algae contain chlorophyll and perform photosynthesis, making them autotrophic.

• (B) Mushroom – Incorrect; mushrooms are fungi and obtain nutrients by decomposing organic matter (heterotrophs).
• (C) Grasshopper – Incorrect; grasshoppers consume plants (heterotrophs).
• (D) Butterfly – Incorrect; butterflies feed on nectar and cannot produce their own food (heterotrophs).