Chemistry

Question Analysis
This question involves calculating mass number from protons/neutrons and linking it to atomic mass.
The main focus is on the relationship between mass number and approximate atomic mass for isotopes.

Key Concept Explanation
Mass number = protons + neutrons. Atomic mass of an isotope (in amu) is nearly equal to its mass number (since protons/neutrons each ≈ 1 amu, electrons contribute negligible mass).

Step-by-Step Solution
1. Calculate mass number: 7 protons + 8 neutrons = 15.
2. Recall that isotope atomic mass ≈ mass number....