Introduction:
The instrument used to examine the cells of a leaf is a microscope. A microscope is an essential tool for scientists and researchers as it allows them to observe tiny objects and structures that cannot be seen with the naked eye. By using a microscope, we can study the intricate details of cells and understand their functions and characteristics.

Explanation:
Here's a detailed explanation of why a microscope is the correct instrument for examining leaf cells:

1. Magnification:
- A microscope is designed to magnify objects, allowing us to view them in much greater detail.
- Leaf cells are very small, and their structures cannot be seen clearly without magnification.
- The microscope's lenses and eyepiece work together to increase the size of the cells, making them visible to the observer.

2. Resolving Power:
- The resolving power of a microscope refers to its ability to distinguish between two closely spaced objects.
- Leaf cells have various components, such as chloroplasts, nucleus, and cell walls, that need to be observed separately.
- A microscope with high resolving power can distinguish between these structures and provide clear images of individual cells.

3. Types of Microscopes:
- There are different types of microscopes used for examining cells, including light microscopes and electron microscopes.
- Light microscopes use visible light to illuminate the specimen, while electron microscopes use beams of electrons.
- Both types of microscopes can be used to study leaf cells, depending on the level of detail required.

4. Preparation of Leaf Cells:
- Before examining leaf cells under a microscope, they need to be prepared for observation.
- This usually involves obtaining a thin section of the leaf and placing it on a glass slide.
- Staining techniques may also be used to enhance the visibility of certain cell structures.

Conclusion:
In conclusion, a microscope is the instrument used to examine the cells of a leaf. It provides the necessary magnification and resolving power to observe the intricate details of leaf cells. By using a microscope, scientists can study the structure and function of cells, contributing to our understanding of plant biology.