(Principal : School) , (Soldier : Barrack) , (Artist : Troupe) , (Singer : Chorus)
Option:
Justification: In all other pairs, second is a collective group of the first.

(Principal : School) , (Soldier : Barrack) , (Artist : Troupe) , (Singer : Chorus)
Justification: In all other pairs, second is a collective group of the first.