Explanation:

Autotrophs are organisms that can produce their own food through processes like photosynthesis or chemosynthesis, using sunlight or inorganic chemicals. Algae are a type of autotroph because they can perform photosynthesis, using sunlight to produce energy.

Here’s why the other options are not autotrophs:

• (A) Fish: Fish are heterotrophs because they depend on other organisms (such as plants or smaller fish) for food.
• (C) Butterfly: Butterflies are also heterotrophs, as they feed on plants, nectar, or other organisms.
• (D) Mushroom: Mushrooms are fungi and are heterotrophs because they obtain nutrients by breaking down organic matter.

So, algae are autotrophs because they can synthesize their own food using light energy.