4. Which symbol represents a particle that has a
mass approximately equal to the mass of a
neutron?
A a B) B+ C) B- D) p

D) p

Explanation:

The particles listed in the 4 options are:

A) particle: an alpha particle consists of a nucleus of helium, so it contains 2 protons and 2 neutrons. Therefore, its mass is much larger than the mass of a neutron.

B) : this particle is a positron, emitted in a beta-plus decay. A positron is identical to an electron, except that it has positive charge instead of negative. Therefore, it has the same mass as the electron, which is about 1800 times smaller than the mass of the proton and of the neutron.

C) : this particle is a fast-moving electron, emitted in a beta-minus decay. An electron has a mass of , which is much smaller than the mass of the proton or of the neutron.

D) : this symbol represents a proton. A proton has a mass of and has a positive charge. The neutron has a mass very similar to that of the proton (just slightly larger).

So, the correct answer is

D) p