Which of the following is are neutral atoms of carbon and which are isotopes of carbon? (carbon has an atomic number of 6 and an atomic mass of 12)

The correct option is B.
A neutral atom of an element will have the same number of protons, neutrons and electrons; the number of protons and electrons must be the same in order to cancel out their electrical charge.
An element that has different number of protons and neutrons is an isotope. 
From the question given, A has 7 neutrons and C has 8 neutrons while their protons is 6, therefore they are not neutral, they are isotopes. It is only B that has the same number of protons and neutrons.