There are five electrons in third principal energy level of phosphorous atom. The five electrons are distributed over two subshells of the third energy level: 3s and 3p.
Each atom of phosphorus contains 15 electrons. These electrons are arranged in orbitals surrounding the atomic nucleus. The first energy level has a single shell called 1s, which is capable of holding only two electrons. The second energy level has two subshells: 2s and 2p. Eight electrons of phosphorus, therefore, occupy the second energy level, with two electrons occupying the 2s orbital and six in 2p. The remaining five electrons are distributed over two subshells of the third principal energy level with two electrons in the 3s orbital and the remaining three electrons in 3p. The electronic configuration of phosphorus is written as 1s2 2s2 2p6 3s2 3p3.