Grammaticalness: How to use words and phrases like 'per cent of', 'cop' in sentences correctly

In this week’s column, I respond to readers’ queries on grammaticalness. 
Is the phrase ‘per cent of’ followed by a singular or plural verb? The phrase ‘per cent of’ can be used with both singular and plural verbs. If it is followed by a singular countable noun, it takes a singular verb and if it is followed by a plural countable noun, it takes a plural verb. Here are some examples:

Thirty per cent of the city does not face water scarcity.
 Twenty per cent of the students were on leave yesterday.

If the phrase ‘per cent of’ is followed by an uncountable noun (music, advice, information, water, sugar, power, money), it is followed by a singular verb. Here are some examples:

 Ten per cent of water in the sump was pumped up to the tank.
 Only five per cent of the information in the booklet is useful.

Similarly, the phrases ‘half of’, ‘some of’ and ‘a third of’ can be either singular or plural depending on what follows. If they are followed by singular countable nouns, they take singular verbs and if they are followed by plural countable nouns, they take plural verbs. If they are followed by an uncountable noun, it takes a singular verb. Here are some examples:

 Half of the teachers are from Tamil Nadu and the rest are from the other states of India.
 Half of the glass is empty.
 Only a third of the tickets have been sold.
 A third of the class was on leave yesterday.
 Only some of the furniture needs to be repaired.

Is ‘police’ singular or plural? ‘Police’ is always plural. When we talk about an individual member of the police, we use the terms policeman, policewoman, police officer or police chief. Look at these examples:

 Tamil Nadu police arrest ten more activists.
 Police have booked students who created a ruckus on government buses.
 A police officer was suspended for unruly behaviour.
The word ‘cop’ can be used to refer to police officers.
 The cops were watching the criminal’s movements.

Can the word ‘cop’ be used as a plural? The word ‘cop’ can be used as a noun and as a verb. As a verb, the word has two different meanings. The first meaning is ‘to arrest’.

 Three people were copped for possessing drugs.
The second meaning of the word ‘cop’ as a verb is ‘to receive’.
 The young actor copped an award for her role in this movie.