What type turbulence should be reported when it causes changes in altitude and/or attitude more than two-thirds of the time, with the aircraft remaining in positive control at all times

Occasional light chop is the correct answer.

There are six different types of turbulences, such as: light chop, light turbulence, moderate chop, moderate turbulence, severe turbulence, and extreme turbulence. A frequency is considered occasional when its frequency is less than 1/3 of the time. A light chop is defined as a slight, quick and relatively rhythmic bumpiness. In a light chop, there is no much change or plane deviations in attitude or altitude.