Question

multiple - choice question
what is the next step?
✓ add the relative abundances of all three isotopes together.
✓ multiply the mass of each isotope by its relative abundance.
✓ add the masses of all three isotopes together.
✓ divide each isotopes mass by its relative abundance.

Explanation:

Step1: Recall formula for average atomic mass

The formula for average atomic mass \(M = \sum_{i = 1}^{n}m_i\times a_i\), where \(m_i\) is the mass of isotope \(i\) and \(a_i\) is its relative abundance.

Step2: Analyze each option

• Option 1: Adding relative abundances is wrong as they sum to 1 (or 100% in percentage terms).
• Option 2: Multiplying mass of each isotope by its relative abundance is correct as per the formula.
• Option 3: Adding masses of isotopes ignores their abundances.
• Option 4: Dividing mass by abundance is not part of the formula.

Answer:

Multiply the mass of each isotope by its relative abundance.