The correct answer to the question is option 3: nucleus.

The nucleus is a small, dense region at the center of an atom. It contains the protons and neutrons, which make up the majority of the mass of the atom.

Option 1: Electrons are negatively charged particles that orbit the nucleus. While electrons do have mass, it is much smaller compared to the mass of protons and neutrons.

Option 2: Charges refer to the electrical charge of particles. While both protons and electrons have charges, the question specifically asks about mass, not charge.

Option 4: The electron cloud is the region surrounding the nucleus where electrons are likely to be found. It does not contain the majority of the mass of the atom.

It is important to note that while the provided answer is generally correct, it is always a good idea to verify and cross-reference information to ensure accuracy.