Question

1. which part of the atom contributes most to its mass?

a. electrons only
b. protons and neutrons
c. electrons and neutrons
d. protons only

Explanation:

In an atom, electrons have negligible mass (about 1/1836 of a proton's mass). Protons and neutrons are located in the nucleus and have much larger masses compared to electrons. So protons and neutrons together contribute most to the atom's mass. Option A is wrong as electrons have little mass. Option C includes electrons which don't contribute much. Option D is wrong as neutrons also contribute significantly to mass along with protons.

Answer:

B. Protons and neutrons