Each element symbol has two basic numbers, atomic number and mass number. Atomic number, a number in a lower position, states the number of protons, which is typical of each element and is unchangeable. Mass number, placed in the upper position, is a total of protons and neutrons, and is changeable due to difference in neutrons in the isotopes. Thus, a different isotope of chromium must have the same protons (atomic number), but a different mass number.
Within 4 options, we can see that option B is the best, since it has a different mass number from 52, and the mass number is placed on the top.
