Chemistry

Question Analysis
This question evaluates the student's ability to calculate the number of neutrons in an isotope given the atomic number and mass number.

Key Concept Explanation
The mass number (A) is the sum of the number of protons (Z) and neutrons (N) in the nucleus. The relationship can be expressed as .

Step-by-step Solution
1. Identify the given values: atomic number (Z) = 19, mass number (A) = 39.
2. Use the formula to find the number of neutrons (N).
3. Substitute the given values:

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