Correct Answer: Flowers : Bouquet

Solution : Given:
Players : Team (This depicts the relation as the first word is a group for the second word; A group of players is called a team.)

Let's check each option –
First option: Class : Students; A group of students is known as the class.
Second option: Flowers: Bouquet;  A group of flowers is called a Bouquet.
Third option: Grapes : Dozen; A group of grapes is known as a bunch of grapes whereas a dozen is a quantity.
Fourth option: Band : Musician; A group of musicians is known as a band.

So, only the third option follows the same pattern as followed by the given pair. Hence, the second option is correct.