Chemistry

Question Analysis
This question involves using atomic number and neutron-to-proton ratio to identify an isotope (element + mass number).
The main focus is on applying ratio calculations and periodic table lookup to characterize the isotope.

Key Concept Explanation
Atomic number = 15 → element = phosphorus (P, periodic table; sulfur = atomic number 16, eliminate C/D).
Neutron-to-proton ratio = 1.2 : 1 → neutrons = 1.2 × protons.
Protons = atomic number = 15 → neutrons = 1.2 × 15 = 18.
Mass number = protons + neutrons = 15 + 18 = 33.

Step-by-Step Solution
1. Identify element from atomic number 15: phosphorus (eliminate C/Sulfur and D/Sulfur).
2. Calculate neutrons: 1.2...