An atom of an element with atomic number 48 in mass number 120 contains how many electrons

48

Explanation:

So all we have to consider here is the atomic number. Remember that in a neutral atom the amount of electrons = the amount of protons.

Also that the atomic number = the number of protons.

So we can say that in an atom with atomic number 48, there are 48 protons and therefore 48 electrons.