The correct answer is option 2: "It has acquired some electrons from outside."

When a body is charged negatively, it means that it has gained an excess of electrons. Electrons are negatively charged particles that orbit around the nucleus of an atom. In a neutral atom, the number of protons (positively charged particles) in the nucleus is equal to the number of electrons orbiting around it, resulting in a balance of positive and negative charges.

However, when a body gains electrons from outside, the number of electrons exceeds the number of protons. This creates an imbalance of negative charge, resulting in an overall negative charge for the body.

Option 1, which states that the body has lost some of its protons, is incorrect. Protons are not easily gained or lost by a body, so losing protons would not result in a negative charge.

Option 3, which states that the body has lost some of its electrons, is also incorrect. Losing electrons would result in a loss of negative charge, not a negative charge itself.

Option 4, "None of the above," is incorrect as well because the correct answer is option 2.