Element a has 15 protons. determine the number of neutrons in its isotope with mass number 33.
a)15
b)18
c)33
d)48
the answer is b your welcome

In an electrically neuteral atom, number of protons = number of electrons = atomic number.
Mass number = neutrons + protons/electrons/atomic number
Therefore,
neutrons = mass number - protons/electrons/atomic number
Neutrons = 33 - 15 = 18

The answer is thus B. But this is the solution and explanation along with it as proof.