The free energy for the oxidation of glucose to CO2 and water is -686 kcal/mol, and the free energy for the reduction of NAD to NADH is 53 kcal/mol. Why are only two molecules of NADH formed during glycolysis when it appears that as many as a dozen could be formed

The question is incomplete as it does not have the options which are:

a. Most of the free energy available from the  oxidation of glucose is used in the production of ATP in  glycolysis.

b. Glycolysis is a very inefficient reaction, with much of  the energy of glucose released as heat

.c. Most of the free  energy available from the oxidation of glucose remains in pyruvate,  one of the products of glycolysis.

d. There is no CO2 or water produced as products  of glycolysis.e. Glycolysis consists of many enzymatic reactions,  each of which extracts some energy from the glucose molecule.

Most of the free  energy available from the oxidation of glucose remains in pyruvate,  one of the products of glycolysis.

Explanation:

Glycolysis refers to the breakdown of the glucose molecules during the complex process of cellular respiration. The process takes place in ten enzymes catalyzed reactions that form the 2 molecules of pyruvate.

The glycolysis process releases a lot of energy which is measured as -686 kcal/mol. The energy is not released into the reaction directly but is conserved in pyruvate form and less is released into driving the reduction of NAD to NADH.

Thus, the selected option is correct.

x would be the most and the least would be y because there are more fruit   and seeds than flock z has insects

yes, because even though a theory has a  lot of evidence to support it, it is not always true