According to Bohr’s model of the atom, in which orbitals do electrons have the least energy?
The innermost orbital
In the Bohr model, the most stable, lowest energy level is found in the innermost orbit. This first orbital forms a shell around the nucleus and is assigned a principal quantum number (n) of n=1.. Additional orbital shells are assigned values n=2, n=3, n=4, etc.
As electrons move farther away from the nucleus, they gain potential energy and become less stable. Atoms with electrons in their lowest energy orbits are in a "ground" state, and those with electrons jumped to higher energy orbits are in an exicted state
Read more: Bohr Model - Energy, Electrons, Quantum, and Electron - JRank Articles http://science.jrank.org/pages/982/Bohr-Model.html#ixzz3r2UWP34r"excited" state.
The base orbital i.e. the one that is smallest and closest to the nucleus.
According to Bohr's model, as en electron moves from a higher orbital to a lower orbital, and eventually reaches a state where no more energy is released i.e. the electron is in the lowest energy or base orbital, which is the one closest to the nucleus.
EDIT: This answer is very similar to Ghadeer A's answer which must have been posted while I was writing this one. I wil leave this answer up though because the slightly different wording may help someone understand Ghadeer's answer a bit better.