Monosaccharides are generally defined by which of the following carbon to hydrogen to oxygen ratios?
(cho2)n
(c2ho)n
(ch2o)n
(cho)n

The answer is (CH2O)n.

Monosaccharides consists of carbon, hydrogen, and oxygen in ratio 1:2:1.
The basic formula of monosaccharides is (CH2O)n. Let's take for example a glucose, which is monosaccharide. It is known that the formula of the glucose is C6H12O6, which means that it consists of 6 carbon atoms, 12 hydrogen atoms, and 6 oxygen atoms. So, in formula (CH2O)n, it must be n=6, so a glucose can be also represented as (CH2O)6.

It is used to during sexual reproduction between humans

Mitochondria produce atp, a high energy compound. atp is used for all sorts of enzyme-mediated reactions, such as making proteins/nucleotides/etc, certain compounds cross the cell membrane, muscles move, etc.  without this source of energy, a cell will die. it will not be able to repair itself, defend against pathogens, etc.