Which of the following is true concerning operant conditioning principles?
chaining involves reinforcing behaviors that come closer to the target behavior.
shaping involves delivering punishment for unwanted behaviors.
fading involves gradually decreasing the frequency of reinforcement for "not-exactly-right" behaviors.
chaining involves the shaping of the behavior by use of punishment and reinforcement.

Fading involves gradually decreasing the frequency of reinforcement for "not-exactly-right" behaviors.

Explanation:

Fading occurs as time passes, and a conditioned response is no longer reinforced:

Fading also is known as Extinction occurred as Pavlov's dogs were no longer given food, so even if the sound they associated kept ringing, their saliva stopped in the absence of the food after a while. (which initially reinforced the conditioning)

It means that the operant behavior will not result in the reinforcing consequences and making eventually the conditioned behavior to stop happening.

If for any reason  an exctincted behavior reappears again  somehow it has gone through fading , it is called resurgence.