Final answer:
A boron-11 atom has 5 protons in its nucleus, as indicated by its atomic number, which is always consistent for an element.
Step-by-step explanation:
The nucleus of a boron-11 (B) atom contains 5 protons. The atomic number of an element indicates the number of protons in the nucleus, and for boron, this number is always 5, regardless of the isotope. Boron-11 also has 6 neutrons in its nucleus, as indicated by the fact that it is an isotope with a mass number of 11 (protons + neutrons).