Is it if no or if not?
You say "if not". You don't say "if no". In BE, "if no" is relatively common.
How do you write if so?
"If so" means "if that is the case." For example, "Shelby might go to the concert later. If so, she will need a ride." This usage indicates that if Shelby does attend the concert, she will need someone to give her a ride. The phrase functions as a transition, connecting the content of the sentences.
How do you use yes in a sentence?
If yes, make sure to send the form along before the deadline. I wanted to check if you got the email I sent; if so, make sure to send the form along before the deadline. I wanted to check if you got the email I sent; if yes, make sure to send the form along before the deadline.