If you block someone on WhatsApp will they know

When you block someone on WhatsApp, the person will not be notified that they have been blocked.

However, they may notice that they are no longer able to see your profile picture or last seen status, and they will not receive any messages or calls from you.

The messages that you send to them will only show a single tick, indicating that they have been sent but not delivered. They will also not be able to see any updates to your profile or status.