Explanation:

- Lithium is a chemical element with the atomic number 3.

- The atomic number represents the number of protons in the nucleus of an atom.

- Thus, a lithium atom has 3 protons in its nucleus.

Here's a breakdown of the options:

- Option 1: 2 - Incorrect, as lithium has 3 protons.

- Option 2: 4 - Incorrect, lithium has fewer protons.

- Option 3: 5 - Incorrect, this number is more than what lithium has.

- Option 4: 3 - Correct, as it matches lithium’s atomic number.