WhatsApp does not directly allow its users to know if they have been blocked by any of their contacts. But there are ways to know if someone has blocked you on WhatsApp.
You will not be able to view their “last seen” indicator if you are blocked. You will not be able to see their online status in the chat window. But this is not a guaranteed proof that a person has blocked you.
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Now some other ways of knowing for sure that you are blocked is that you will not be able to see changes to the profile picture of a contact. You can cross-check from someone else’s phone who has the same contact to know for sure if there is a difference in profile pictures. However, this tip will only work if the person has changed their profile picture.
Another way to know if a person has blocked you is by sending them a message, if it is marked as sent but not delivered, that’s another indication that you are blocked. Also, any calls you will make will not go through.
But these issues can also be if that person has no internet connection, so again it is not a guarantee, so you can crosscheck with someone else.
Now if you want to block someone on WhatsApp you can either open your chat with that contact tap their name and then block them by choosing block contact.
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Also, you can go to Settings, Account, Privacy, Blocked and then select a contact to block.