The force causing the centripetal acceleration when the coin is stationary relative to the rotating turntable is static friction.
The question pertains to the force causing the centripetal acceleration when the coin is stationary relative to the rotating turntable. When the coin slips, it indicates that the force acting towards the center of the turntable is unable to maintain the circular path, which is necessary for centripetal acceleration. This force, up until the point of slipping, is provided by static friction.
Once the coin begins to slip, the force responsible for maintaining its circular motion would be kinetic friction, but it is insufficient to keep the coin moving in a circle. Therefore, the force causing the centripetal acceleration when the coin is stationary relative to the turntable is static friction. There is no physical force called centrifugal force; rather, it is an apparent force observed from the rotating frame of reference.