Question

In which of these cases do we have enough information to say that the atom is electrically neutral?

A. The atom has 4 neutrons and 4 protons.
B. The atom has 7 protons and 7 electrons.
C. The atom has 19 electrons and 19 neutrons.
  D. 

The atom has 15 neutrons and 15 electrons.

Answer 1

b. 7 protons and 7 electrons, just took the test

Answer 2

So we want to know when do we have enough information about the atom that we can say that it is electrically neutral. So the information we need to know is the number of protons, whic are positively charged particles and the number of electrons which are negatively charged particles. Number of protons has to be equal to number of electrons for the atom to have neutral charge. Neutrons are electrically neutral so their number doesn't change the charge of the atom. So the correct answer is B.