A mineralocorticoid is

Options

A. Testosterone
B. Aldosterone
C. Androgen
D. Progesterone.

Answer

### Step-by-Step Solution:

1. **Identify the Category of Hormones**: Understand that mineralocorticoids are a class of steroid hormones that are primarily involved in the regulation of mineral balance in the body, particularly sodium and potassium.

2. **Review the Options Provided**: The options given are:
- Estrosterone
- Aldosterone
- Androgen
- Progesterone

3. **Analyze Each Option**:
- **Estrosterone**: This is an estrogen hormone, which is primarily involved in female reproductive functions.
- **Aldosterone**: This is a mineralocorticoid hormone produced by the adrenal cortex and is crucial for regulating sodium and potassium levels in the blood.
- **Androgen**: This refers to a group of hormones, including testosterone, that are primarily male sex hormones.
- **Progesterone**: This is a sex hormone involved in the menstrual cycle and pregnancy, produced by the ovaries.

4. **Determine the Correct Answer**: Based on the analysis, the only hormone that fits the definition of a mineralocorticoid is **aldosterone**. It is specifically known for its role in regulating mineral metabolism and maintaining sodium and potassium balance in the body.

5. **Conclusion**: Therefore, the correct answer to the question "A mineralocorticoid is" is **aldosterone**.