Question

A reduction in $O_2$ evolution occurs when light wavelength is

• A. More than 680 nm
• B. Less than 680 nm
• C. Less than 660 nm
• D. 560 nm

Answer 1

The correct option is A More than 680 nm

A) Photolysis of water takes place in PS II where wavelengths of light up to 680 nm is used. Anything more than that wavelength will not be effective in splitting water to produce oxygen.
B) Wavelengths less than 680 nm are optimum for oxygen evolution.

C) Wavelengths less than 660 nm are optimum for oxygen evolution.
D) The threshold value for PS II is 680 nm.

So the correct answer is 'More than 680 nm'.