Isotope Worksheet Answer Key - ISD 622 Isotope Practice Worksheet Name: 1. 2. D. 4. 13 12 Here are three isotopes of an element: a. The element is: b. The number 6 refers to the c. The numbers 12, 13, and 14 refer to the d. How many protons and neutrons are in the first isotope? (O e. How many protons and neutrons are in the second isotope? f.