Question

Boron has two stable isotopes, $10B$ (19%) and $11B$ (81%). The atomic mass that should appear for boron in the periodic table is

• A. 10.8
• B. 10.2
• C. 11.2
• D. 10.0

Answer 1

Answer: (A)

10.8

Answer 2

Atomic mass $= \frac{10 \times 19 + 81 \times 11}{100} = \frac{190 + 891}{100}$ $= \frac{1081}{100}$

$= 10.81$