LET'S TAKE IT ONE BY ONE:
a. It has a negative charge.
WRONG. Electron has a negative charge. Neutron has neutral charge/ has no charge.
b. Its mass is much greater than the proton.
Their masses are close enough.
c. It is found in the nucleus.
Neutron is found in the nucleus of an atom together with the proton.
d. the number of neutrons is called the mass number.
Mass number is the number of protons and neutrons of an atom -- so not only neutrons but also protons.
Which of the following best describes a neutron?
The answer is C.