Answer:
2p
Explanation:
Boron is a member of group 13. The highest energy sub-level is usually found on the outermost shell of the atom of the element involved.
For a group 13 element, its outermost shell configuration is ns2 np1. The electronic configuration for boron is; 1s2 2s2 2p1.
Hence the highest energy sub-level in boron is 2p.
