Chemistry

Question Analysis
This question evaluates the student's understanding of the concept of mass number, which is the sum of protons and neutrons in an atom.

Key Concept Explanation
The mass number of an isotope is calculated by adding the number of protons and neutrons in the nucleus.

Step-by-step Solution
1. Identify the number of protons: 20
2. Identify the number of neutrons: 22
3. Calculate the mass number: 20 + 22 = 42
4. The...