The most common isotope of chromium has a mass number of 52. Which notation represents a different isotope of chromium?

a. 52/25Cr

b. 54/24Cr

c. 24/32Cr

d. 24/54Cr

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.