The relative atomic mass of Boron is 10.81. The naturally occurring isotopes are 10 extB and 11 extB. a) Which isotope is more abundant? b) Explain why the relative atomic mass of an element is never

a) The relative atomic mass (RAM) of Boron is given as 10.81. The two isotopes are $^{10}\text{B}$ and $^{11}\text{B}$. The RAM is a weighted average of the masses of its isotopes. Since 10.81 is closer to 11 than it is to 10, the isotope with the mass number 11 must be present in a higher proportion.

The more abundant isotope is $\boxed{\text{}^{11}\text{B}}$.

b) The relative atomic mass of an element is never a whole number because it is the weighted average of the masses of all its naturally occurring isotopes. Most elements exist as a mixture of two or more isotopes, each with a different mass number and a specific natural abundance. This averaging process, combined with the fact that the exact mass of protons and neutrons is not precisely 1 atomic mass unit, results in a non-integer value.