is whatsapp safe?

Yes and No.

Whatsapp messages are encrypted so that means no one can become a middle man and read them. Not your government, not your ISP etc. They would have to hack your phone to do it so you are weak point not whatsapp.

On the other hand they are owned by Facebook so you can be damn sure they are using all your chats for some sort of advertising and will also hand your data over to authorities if needed be.