The trend for ionization energy is a general increase from left to right across a period. however, phosphorus (p) is found to have a higher first ionization energy value than sulfur (s). explain this exception to the general trend in terms of electron arrangements and attraction/repulsion.

₁₅P 1s²2s²2p⁶3s²3p³
₁₆S 1s²2s²2p⁶3s²3p⁴
It is because: 1) phosphorus have 3 unpaired electrons in 3p shell, and that is more stable than 3p⁴ in sulfur, so it ie easier to remove 1 paired electron in sulphur to became 3p³.
2) repulsion in 3p shell in sulfur between 2 paired electrons is higher, so it is easier to remove that electron.