The chromophore of higher plant phytochrome is:
C fits best: Phytochromobilin. Keep the PHYTOCHROME basics straight and Phytochromobilin stands out as the precise answer. Avoid: A) Biliverdin; B) Chlorophyll; D) Flavin. Light and flowering items often hinge on which photoreceptor or day-length rule is in play.
Ref: Best CSIR NET Plant Physiology books: Master Unit 6 with Taiz & Zeiger and Salisbury & Ross. Crack Part C experimental questions with top textbooks.