A lithium atom with a mass number of 7 (i.e., 3 protons and 4 neutrons in its nucleus) would have the electronic configuration of 1s²2s¹.
The outermost orbital (ring) of this lithium atom is the second energy level, which consists of a single s orbital (2s). The 2s orbital can hold up to two electrons, but in this case, there is only one electron in the 2s orbital since lithium has only three electrons.
Therefore, there is 1 electron in the outermost orbital (ring) of a lithium atom with a mass number of 7.