The psychologist who formulated the principles of operant conditioning was

A) John B.Watson.
B) Sidney Pressey.
C) B.F.Skinner.
D) Ivan Pavlov.

B.F. Skinner is credited with formulating the principles of operant conditioning, which focus on how an organism's behavior can be modified by consequences such as rewards and punishments. John B. Watson was a behaviorist who studied classical conditioning, while Sidney Pressey was an educational psychologist who developed a mechanical teaching machine. Ivan Pavlov was a physiologist who conducted research on classical conditioning with dogs.