Question

cristae create a large surface area for which generating reactions

Answer 1

Since the options are not given, I am giving a general answer.

The correct answer should be - To generate energy.
The reactions involved should be the oxidative phosphorylation. In these reactions, oxygen is utilized to meet the ATP demands of the cells and so it needs a large surface area to facilitate the rapid production of energy at a high rate.
Also, the folding in the cristae of the mitochondria provide a larger surface area for more exchange of ions and proteins.

Answer 2

Answer:

The cristae create a ‘large surface area’ for reactions that involve the high production of ATP (Adenosine triphosphate).  

Explanation:

The Cristae folding form an integral part of inner membrane of the ‘mitochondria’. Mitochondria is termed as the ‘power house’ of the cell which produces the cells entire ATP. The number of cristae is higher in mitochondria of cells that produce high amount of ATP. A metabolically active cell requires high amount of ATP.