Which or That

Here is some help for RC in CAT. Many people find it difficult to understand the subtle differences of word usage. So here is a series starting today that will try and explain the difference in usage of the commonly used words

The first in the series will be 'which' or 'that'
1. Many times they can be used interchangeably

2. 'that' is usually used in a less formal sense

3. Most importantly, 'that' can be used only for restrictive relative clauses, while 'which can be used for both restrictive and non-restrictive relative clauses.
Restrictive clauses put a restriction on the noun that they are talking about and make that noun specific. E.g., "The ball, which is red, is broken". In this sentence, 'which' can be replaced by 'that'
Non-restrictive clauses just give additional info about the noun. This additional information can be even dropped without affecting the sentence. E.g., "The one horned rhino, which lives in the forests of India, is becoming extinct". In this sentence 'which' cannot be replaced by 'that'. Note that this is a non-restrictive clause because we are not referring to a particular rhino and hence it is non-restrictive.

Any queries on the usage of which and that, put them in the comments. There will be more to come tomorrow.