Explanation:

- The phrase "One who makes an active effort to promote human welfare" refers to someone who is dedicated to improving the well-being of humanity through generous actions or donations.

- Option:1, Philanthropist: A philanthropist is someone who actively works to promote human welfare, often through charitable donations and initiatives.

-

- Option:2, Philosopher: A philosopher is someone who seeks wisdom or knowledge and often explores questions about existence, ethics, and reason.

- Option:3, Philanderer: A philanderer is a person who engages in casual romantic or sexual relationships with many people, often disregarding commitments.

- Option:4, Physicist: A physicist is someone who studies or specializes in physics, the science concerned with the properties of matter and energy.

Hope this clarifies each option's meaning!