Final answer:
A boron atom with an atomic number of 5 and an atomic mass of 11 contains 5 protons, 5 electrons, and 6 neutrons.
Step-by-step explanation:
An atom of boron has an atomic number of 5 and an atomic mass of 11. The atomic number tells us that there are five protons in the nucleus of a boron atom. Given that the atomic mass is the sum of the protons and neutrons, and the atomic mass of boron is 11, we can deduce that there must be 6 neutrons (11 - 5 = 6). Boron atoms also have an equal number of electrons as protons when they are neutral. Therefore, the correct composition of a neutral boron atom is 5 protons, 5 electrons, and 6 neutrons.
Boron has two naturally occurring isotopes, boron-10 and boron-11, which differ only in their number of neutrons. Isotopes are variants of the same element that have the same number of protons but a different number of neutrons. Boron's average atomic mass is calculated based on the relative abundance of its isotopes: 20% boron-10 (5 protons and 5 neutrons) and 80% boron-11 (5 protons and 6 neutrons).