I think I have found the best explanation :

Fact: People often misuse who and whom.

*Remember: Who is in nominative case, like he is, whereas whom is in objective case, like him is.

Examples: (Who, Whom) is going to the beach? He is going to the beach = Who is going to the beach?
To (who, whom) shall I write the check? This is a little trickier-please follow.
"¢ Change the question to a statement and substitute he or him, whichever fits:
I shall write the check to him = I shall write the check to whom = To whom shall I write the check?

** Sometimes in English we separate prepositions from their objects, which makes it a bit trickier.
Example: (Who, Whom) are you going to the awards ceremony with?
"¢ Rearrange the sentence so that it is in standard Subject-Verb-Complement order, and substitute he or him.
You are going to the awards ceremony with him = You are going to the awards ceremony with whom =
Whom are you going to the awards ceremony with?

*** In English, sentence structure can complicate matters. In complex or compound-complex sentences, you need to make sure that the clause with the who/whom choice is in standard Subject-Verb-Complement order.

Example: I must meet the person (who, whom) she recommended.
"¢ Isolate each clause: I must meet the person (independent clause); (who, whom) she recommended - dependent clause
"¢ Rearrange who/whom clause so it's in S-V-Complement order: she recommended (who, whom)
"¢ Substitute as before: she recommended him = she recommended whom
"¢ Change the order back: I must meet the person whom she recommended.

Who and whom is confusing-this might help. In your mind, rewrite just the part of the sentence that contains who or whom. Instead of who use he. Instead of whom, use him. See which one sounds better. If him sounds better, use whom in the original sentence. Otherwise, use who.

Answers:
There is a fifty-dollar reward for whoever finds and returns my dog.
There will be a five-minute break for whoever among you needs it.
Can you tell whom she looks like?
Give these old coats to whoever seems to need them most.
whom shall I say is calling?
The teacher seemed to flunk whomever she didn't like.

confuse mind wrote:Please provide the answer along-with the reasoning

There is a fifty-dollar reward for (whoever, whomever) finds and returns my dog.
There will be a five-minute break for (whoever, whomever) among you needs it.
Can you tell (who, whom) she looks like?
Give these old coats to (whoever/whomever) seems to need them most.
(who/whom) shall I say is calling?
The teacher seemed to flunk (whoever/whomever) she didn't like.

The above sentences have some peculiarity because of which I got confused.
- these sentences are made up of more than 1 clause
- one clause is asking for objective form and the other clause is asking for subjective form. Thus, a confusion which one is to be used.

Please help!