Answer is: number is 0.14303691.
Carbon-13 (¹³C) is a stable isotope of carbon with mass number 13, it has six protons and seven neutrons.
Isotopes are chemical elements with same atomic number, but different mass number (different number of neutrons).
ω(¹³C) = 1.10% ÷ 100%.
ω(¹³C) = 0.0110; abundance of carbon-13 in nature.
m(¹³C) = 13.003355; the atomic mass of carbon-13.
ω(¹³C) · m(¹³C) = 0.0110 · 13.003355.
ω(¹³C) · m(¹³C) = 0.14303691.
