We can use either a singular verb or a plural verb with a Collective Noun, means it’s optional. However, if it’s clear from  the context that the collective noun is referring to a single group or unit we use a singular verb, and if the collective noun is referring to a number of individuals separately we use a plural verb. Some of the collective nouns are

1. a) A crew of 90 takes care of the 300 passengers on the ship.
b) The crew were arrested on a charge of smuggling.

2. a) The finance committee controls the school’s budget.
b) The committee are considering the proposal.

3. a) The government is spending crores of rupees in its attempt to control terrorism.
b) The government are expected to announce their tax proposals today.

4. a) The public has a right to know about this.
b) The public were fighting among themselves.

5. a) An unruly mob has gathered outside.
b) The mob were scattered in all directions. (means members constituting the mob)

6. a) Our cricket team is strong enough.
b) The team are fighting among themselves. (Here THE TEAM = the players of the team]

NOTE: But some of the above collective nouns such as Army, Audience, Class, Committees, Choir, Club, Congregation, Family, Firm, Flock, Government, Teams, etc. also take A/AN in their singular use, and form their plurals by the addition of a/es/ies; e.g.