Red drop proposed by Emerson and Arnold indicated that - Sri Chaitanya Infinity Learn Best Online Courses for NCERT Solutions, CBSE, ICSE, JEE, NEET, Olympiad and Class 6 to 12

A
photosynthetic yield was minimum when monochromatic beam of more than 680nm was supplied to the plant.
B
photosynthetic yield was maximum when monochromatic beam of more than 680nm was supplied to the plant.
C
photosynthetic yield was minimum when monochromatic beam of 680 nm was supplied to the plant.
D
photosynthetic yield was minimum when polychromatic beam was supplied to the plant.

Solution:

Supplying light of wavelength more than 680 nm result into functioning of only PS I but not PS II. It produced only ATP but not NADPH₂. Hence there is decline in O₂ evolution and CO₂ fixation resulted in decrease in photosynthesis.