Chapter 16, Problem 9STP

To determine

To Choose: The correct option. 

Answer to Problem 9STP

Option C

Explanation of Solution

Introduction:

The mass number of an atom defined as the sum of neutrons and protons present in it. (Or isotopes of an element). The atomic number is equal to the number of protons present in the nucleus of the element (or isotopes of an element).

Nickel is the naturally occurring stable element which is present in five isotopes. They are 58-Ni, 60-Ni, 61-Ni, 62-Ni, and 64-Ni. 

All these isotopes of nickel have different atomic mass, but they have the same atomic number as the number of neutrons is different for different isotopes for the nickel element. The number of protons is the same for all the isotopes of the nickel element. The atomic number based on the number of protons (so, the number of protons is equal to its atomic number).

The atomic mass or mass number is the sum of protons and neutrons therefore, the isotopes of nickel have a different mass. 

Conclusion: 

The isotopes of elements have same atomic umber because the atomic number measured by the number of protons only for every element but each element has different mass because the neutrons vary in isotopes of the element.