If an atom has the electron configuration 1s22s22p 1, how many electrons must it gain to achieve an octet?

According to octet rule element has eight electrons in its valence shell. This give it the same electronic configuration as a group 18 elements. Atom with electronic configuration 1s2 2s2 2p1 require five electrons to achieve octet. This is because the valence electrons are 3 in 2s2 and 2p1 and hence require 5 electrons to be filled.