There are five interrogative pronouns, and they are used for asking questions:
There are three things you need to know about interrogative pronouns.
1. Interrogative pronouns often lack an antecedent because the noun they refer to is found in the answer to the question:
Who shot John F. Kennedy? Lee Harvey Oswald.
2. The pronoun whom is reserved for the object of a preposition or verb:
To whom did you sell your old truck?
Whom will Sally marry?
Few people actually use whom in everyday conversation, and in less formal writing who is sometimes acceptable.
3. You can add emphasis to your interrogative pronoun by adding –ever at the end (e.g., whoever).
Relative pronouns relate extra information, usually in the form of a relative clause. Here are all five relative pronouns.
Note that with the exception of that, these are the same as the interrogative pronouns. It’s just their function that’s different.
We tend to use who for people, which for things, and that for people or things, though there are exceptions. Here are few examples of relative pronouns in a sentence:
The Tragically Hip, who went on their last tour in 2016, have long been an iconic Canadian band.
I ran into Jenny, whom you dated in high school.
Jupiter, which is the largest planet in our solar system, is still tiny compared to the sun.
I love those socks that you wore yesterday.
As mentioned earlier, whom has fallen into disuse. It is properly used as the object of a verb or preposition, but in casual speech is typically replaced by who.