Frog mainly excretes

Options

A. Ammonia
B. Uric acid
C. Citrulline
D. Urea

Explanation

### Step-by-Step Solution:

1. **Understand the Question**: The question asks what nitrogenous waste is primarily excreted by frogs.

2. **Identify the Types of Nitrogenous Waste**: There are three main types of nitrogenous waste excretion:
- **Ammonotelic**: Organisms excrete ammonia. This is common in aquatic organisms like protozoans and cnidarians.
- **Uricotelic**: Organisms excrete uric acid. This is typical for birds and some insects.
- **Ureotelic**: Organisms excrete urea. This is seen in mammals, including humans.

3. **Determine the Excretion Method of Frogs**:
- **Adult Frogs**: Adult frogs are classified as ureotelic, meaning they primarily excrete urea.
- **Larval Stage (Tadpoles)**: In contrast, tadpoles, which are aquatic, excrete ammonia and are classified as ammonotelic.

4. **Select the Correct Answer**: Since the question does not specify the stage of the frog, but generally refers to frogs, the answer is based on the adult frog's excretion method. Therefore, the correct answer is **urea**.

5. **Review the Options**:
- Ammonia: Incorrect for adult frogs.
- Uric Acid: Incorrect for adult frogs.
- Citrulline: Incorrect; it is an intermediate in the nitrogen cycle.
- Urea: Correct answer for adult frogs.

### Final Answer:
Frog mainly excretes **urea**.

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