The scientist who discovered the cell:

1. Robert Hooke

2. Leeuwenhoek

3. Robert Brown

4. Knoll and Ruska

The correct option is A

Robert Hooke

The correct option is A:

Explanation of the correct option:

1. Robert Hooke first discovered the existence of cells by observing the cork of a plant using a microscope.

Explanation of the incorrect options:

Option B:

1. Anton von Leeuwenhoek, with the help of a more advanced microscope, discovered living cells when he observed a drop of pond water.

Option C:

1. Robert Brown discovered the existence of the Nucleus.

Option D:

1. Max Knoll and Ernst Ruska are related with discovery of the Electron microscope.

Final answer: The scientist who discovered the cell: Robert Hooke.