In chromium-50 there are 26 neutrons, because 26 + 24 = 50.
In chromium-52 there are 28 neutrons, because 28 + 24 = 52.
In chromium-53 there are 29 neutrons, because 29 + 24 = 53
Remember the atomic number, identifies elements it is different for every element and it is the number of protons in that element. So by adding that to the number of neutrons you can get the mass number.
