Words given on the left side of (::) are related with each other by some Logic/Rule /Relation. Select the missing word/word pair on the right side of (::) from the given alternatives based on the same Logic/Rule/Relation.

Army : Soldiers :: Shoal : ?

Fish

Logic here is :

Army : Soldiers

Group of Soldiers is called Army .

Similarly ,

Shoal : ?

Group of Fish is called Shoal .

Fish is correct answer .