Boron has two isotopes & whose relative abundances are 20% & 80% respectively

CHEMISTRY · Single correct · A Level · Chemistry · Atomic structure · Atomic structure

Problem

Boron has two isotopes

\text{B}^{10}

\text{B}^{11}

whose relative abundances are 20% & 80% respectively. What is the avg. atomic weight of Boron? (1) 10 (2) 11 (3) 10.5 (4) 10.8