The convex lens is used in-

Options

A. Microscope
B. Telescope
C. Projector
D. all of the above.

Explanation

To solve the question regarding the use of a convex lens, we can analyze the applications of convex lenses in various optical instruments.

### Step-by-Step Solution:

1. **Understanding Convex Lens**: A convex lens is a lens that is thicker in the middle than at the edges. It converges light rays that are initially parallel to the optical axis.

2. **Applications of Convex Lens**:
- **Microscope**: A compound microscope uses both convex and concave lenses. The convex lens is used to magnify small objects.
- **Telescope**: In telescopes, convex lenses are used to gather light and magnify distant objects. They are typically used in combination with concave lenses.
- **Projector**: Projectors use convex lenses to focus and enlarge images onto a screen.

3. **Conclusion**: Since convex lenses are utilized in microscopes, telescopes, and projectors, we can conclude that the correct answer to the question is that a convex lens is used in all of the mentioned devices.

4. **Final Answer**: Therefore, the answer is **D) All of the above**.