How many neutrons are in barium-137

a-137
b-81
c-112
e-56

Barium has 81 neutrons, along with 56 protons and 56 electrons. 

Since Barium has an atomic number of 56, that means that the protons and electrons will also have 56. Barium has an atomic mass of 137.327. We can round it to the whole number and then subtract it by our atomic number of 56. The rounded number would be 137, so now we can subtract 137 - 56 to get 81, which is how many neutrons are in Barium.