i am trying to log in my yahoo mail but its saying wrong password every time though its the right password.

Can you log into your account on the Yahoo email web site using that password? While on the website have you tried using the reset password or forgot password option to create a new password to see if the Mail application will accept the new password?

If necessary, try deleting the account from the Mail application, quit/reopen Mail, and then add the account back.

In addition to Eric Root's suggestions, you could also check whether your Yahoo account is protected and requires an app-specific password: https://www.lifewire.com/manage-app-passwords-imap-pop-yahoo-1174448