Question

Neon occurs as two isotopes of mass numbers 20 and 22. Its relative atomic mass is 20.2. What is the percentage of ²⁰Ne in naturally occurring neon?

• A. 90
• B. 80
• C. 20
• D. 10

Answer 1

The correct option is A

90

Solution

We can use the formula:

Average atomic mass of Ne = [(Atomic mass of X₁) x (% of X₁)] + [(Atomic mass of X₂) x (% of X₂)]

100 100

20.2 = (20 x X ) + [22 x (100 - X)]

100 100

2020 = 20X + 2200 - 22X

2X = 180

X = 90%