\(^{10}_5 B\)
An atom of this isotope contains 5 protons and 10-5=5 neutrons.
\(5 \times 1.6726 \times 10^{-27} + 5 \times 1.6749 \times 10^{-27} = \\
8.363 \times 10^{-27} + 8.3745 \times 10^{-27}= \\
16.7375 \times 10^{-27}= \\
1.67375 \times 10^{-26} \approx \\
1.67 \times 10^{-26}\)
The answer is A. 1.67 × 10⁻²⁶ kg.