4 would be an acid 9 would be a base 7 is neutral. Anything higher is a base. Anything lower is an acid. For example a 1 would be super acidic - like eat the flesh off your body.
Acidic zone is a zone with pH equal in the interval 0 < pH < 7 Basic zone is a zone with pH equal in the interval 7 < pH < 14 So, the answer for your question is 4 because it is in the interval 0 < pH < 7 Good luck!
