An atom has a proton mass of 35, a neutron mass of 35, and an electron mass of 3. What is the estimated mass of the atom?

A. 35 B. 70 C. 38 D. 73

The answer is therefore B. 70 (35 protons + 35 neutrons)

The mass of an atom (its atomic mass) depends upon the sum of the number of protons and the number of neutrons present in the nucleus.

The answer is therefore B. 70 (35 protons + 35 neutrons)

Electrons do have SOME mass but it is almost 2000 times less than the mass of a proton. Therefore the electrons mass is insignificant as there aren't enough electrons to affect the total mass in any stones we know about.