Question

Which of the following describes a similarity and a difference between isotopes of an element?

a. same atomic number; different number of protons

b. same number of protons; different atomic number

c. same atomic number; different mass number

d. same mass number; different atomic number

e. same number of neutrons; same number of protons

Answer 1

Isotopes of an element are defined has that has same atomic number but different mass number mean they have different number of neutrons
so the statement that best describe a similarity is 
 same atomic number; different mass number
so correct option is C 
hope it helps