Which neutral atom is isoelectronic with o+?

Isoelectronic means equal number of electrons.

O+ is formed when the atom of O loses 1 electron.

The number of electrons of neutral O atom equals its number of protons.

Number of protons identifies the atomic number and position of the element in the periodic table.

The positon of O in the periodic table is A = 8, so it has 8 electrons and O+ has 8 - 1 = 7 electrons.

The neutral atom with one electron less than O is of the element to the left of O in the periodic table (A = 7). That element is N.

Therefore, the neutral atom isoelectronic with O+ is N (both have 7 electrons).