• What is Hill reaction ?and where does it occur :
• Absence of water
• Total darkness
• High altitude plants
• Presence of ferricyanide

Hai,
Ferri cyanide is the answer
It is an experimental induced Light reaction.

Hill reaction is used to study the rate at which light energy is converted to chemical energy under darkness
and by giving limited light, when we want to measure the energy assimilated.
So total darknessis the not answer as we are using light to measure.

Water is compulsory required to release hydrogens during splitting of Water.

In this reaction to acess the energy absorbed
finally we use Ferricyanide as hydrogen absorber.
So ferricyanide is the correct answer