English Grammar -- Who did you meet? or Whom did you meet?

I think many ESL students like me find difficulty in using “who” and “whom”. I wrote some information that can help you to understand and use both of them in a correct way.
First of all, who and whom are relative pronouns. Also, who is a subject relative pronoun and whom is an object relative pronoun. This means we use “who” when we want to give extra information about the subject and we use “whom” when we need to provide additional information about the object.
This can be understood by looking into these examples,

Image Credits

WHO

“The girl who is wearing red shirt is my sister.”
“There is someone who wants to meet you.”
“A student who has taken the test on the same day of yours got the results.”
“ Jay, who teaches the English language, is getting married soon.”

Here the pronoun (who) right after the noun or person denotes the subject. So who is a subject tries to give extra information about the person. Moreover, the subject “who” is doing the action.

WHOM

Whom, on the other hand, receives the action. And often “whom” is followed by the someone who is performing the action.
“Sheela, whom I have known for several years, is visiting us tomorrow.”
Here, Sheela is receiving an action from “I.”

“Nelson Mandela is someone whom most people admire.”
The action is being performed by most people, and it is being received by “Nelson Mandela”.

The key here is whenever whom comes we need to add a subject like a pronoun or a person's name after the word “whom” that performs as the subject, whereas who itself acts as a subject and we use verb right after the word “who”, so it shows the action.

However, in some cases, where we use the passive voice, whom is not followed by a subject.
“Nelson Mandela is someone whom is admired” This sentence is in passive form, and it is understood that the extra information is “ by many people”.

WHO and WHOM with Quantifiers

Quantifiers give us information about the sum or the percentage that involves quantity.
“ My friends, most of whom are from Australia, is visiting us next month.”
“ There are many people here today, five of whom I know.”

These are adjective clauses that are included with quantifiers.
The structure is “ quantifier + of + whom + information.
The key here is, we are not supposed to say who in this case. Always say “ Whom.”

Question Form

“ Who entered the classroom first?”
“Who cooked this food.”
“Who is more pretty.”

Here, “who” did the action, so it is correct. The thing we need to remember here is who is Performing action and the answer will be the person who represents “ who”.

“ Whom did you beat yesterday.”
Here, Whom is receiving the action and “you” is performing the action. So we have to use Whom.
“Whom are you inviting.”
“Do you know who got the first price.”
Here, “Who” is performing an action.
“Do you know whom she is talking with” apparently, she is performing action and not “you.”

The other thumb rule here is when you get the answer for the question is one of these ”him, her, them” then use “Whom” or if you get “he, she, they” then use “who.”
For example “who is more pretty” the answer will be “She is pretty” so I used Who
“ Whom did you beat yesterday” the answer will be “ I beat him.”
In the above examples we cannot say “her is pretty” and “ I beat he”