The relative atomic mass of an element is the average mass of the atoms of that element, taking into account the relative abundances of its different isotopes. Isotopes are atoms of the same element that have different numbers of neutrons in their nuclei.
Boron has two naturally occurring isotopes: boron-10 and boron-11. Boron-10 has 5 protons and 5 neutrons, while boron-11 has 5 protons and 6 neutrons. These isotopes exist in different proportions in nature, with boron-10 being more abundant.
The relative atomic mass of boron is calculated by taking the weighted average of the masses of these isotopes, based on their relative abundances. Since boron-10 is more abundant, it contributes more to the overall atomic mass of boron. Therefore, the relative atomic mass of boron is not a whole number but falls between the masses of boron-10 and boron-11.
the relative atomic mass of boron is approximately 10.81. However, please note that the atomic weights of elements can be subject to slight variations as more precise measurements are made or new data becomes available.