The correct option is (c) photoperiodism.
Explanation:
Phytochrome is a chromoprotein (photosensitive pigment) that exists in two states, pr (red) or P660 and Pfr, (far red) or P730.
Phytochrome is involved in photomorphogenetic responses, seed germination, bud dormancy, synthesis of gibberellin and ethylene and photoperiodism.