Question

Two atoms are isotopes of the same element. Which of the following should
be different for these two atoms?
A. The behavior in a chemical reaction
B. The number of neutrons
C. The type of element
D. The number of protons

Answer 1

Answer:

Isotopes are atoms with different atomic masses which have the same atomic number. The atoms of different isotopes are atoms of the same chemical  element; they differ in the number of neutrons in the nucleus.

In short the answer is B

Answer 2

For short Answer is B : the number of neutrons