Which is correct? `A small percentage of the students is worked up about the fee hike’ or `A small percentage of the students are worked up……..’?

People who are fond of grammar would argue that when the word `percentage’ is preceded by the definite article `the’, then the verb is usually singular. It doesn’t really matter if the noun preceding the verb is singular or plural.
*The percentage of students from Delhi is relatively small.
Although the noun (`students’) is plural, the verb that follows (`is’) is singular.
*The percentage of people willing to participate keeps decreasing every year.

When you talk about `a percentage’, on the other hand, it can be followed by a singular or plural verb. It depends on the noun which follows `percentage’.
*A very small percentage of the students are from Delhi.
*I’m told that a small percentage of Padma’s income goes to charity.

Source: ‘Know Your English’ (The Hindu) – August 07, 2006 

Why do we say, `the U.N’, but not `the UNESCO’?

When you use the abbreviated form of a well-known organisation and you pronounce each letter separately, then you use `the’. In the case of `U.N’, for example, you pronounce the `u’ as well as the `n’ separately. Other famous organisations which have to be preceded by `the’ are `BBC’, `CBI’, `FBI’ and `EC”. In the case of UNESCO, the letters are not pronounced individually. You put them together and say it as a word. When the abbreviated form of an organisation is pronounced as a word, then you need not put `the’ before it. In the case of `OPEC’, `UNICEF’, and `NATO’, there is no need for the definite article `the’.

Source: ‘Know Your English’ ( The Hindu) – April 3, 2006

Is it OK to say, `The President Abdul Kalam visited Chennai last week’?

If you want to include an individual’s name with titles like `Queen’, `King’, `Prime Minister’ and `President’, then you normally don’t use the definite article `the’.

For example, we do not say, `The Queen Elizabeth drank coffee’. We can either say, `The Queen drank coffee’ or `Queen Elizabeth drank coffee’. Your sentence is therefore wrong. You can either say, `The President visited Chennai last week’ or `President Abdul Kalam visited Chennai last week.’

Source: The Hindu ‘Know Your English’ Series, December 19, 2005