How many protons are there in a lithium nucleus ?

3

The correct answer is option (4) 3.

The number of protons in an atomic nucleus is equal to the atomic number of the element. For lithium (Li), the atomic number is 3. This means that a lithium nucleus contains 3 protons.

In general, the atomic number represents the number of protons in an atom, and it also determines the element's identity. The nucleus of an atom contains both protons and neutrons. Protons carry a positive charge, while neutrons have no charge.

So, for lithium:

Atomic Number (Z) = 3

Number of Protons = 3

This is a fundamental principle in atomic structure, and it helps distinguish one element from another based on the number of protons in the nucleus.