The ninth reaction involves the conversion of 2-phosphoglycerate into phosphoenolpyruvate. The enzyme enolase, which produces a double bond by removing the hydroxyl group on 2-phosphoglycerate catalyzes this reaction. Note that the resulting molecule is an enol (double bond -ene, and alcohol - ol).

Isomerases catalyze the isomerization, or rearrangement of atoms within a molecule, of its substrate. Isomerases are seen in glycolysis inn the second step where glucose-6-phosphate is converted into fructose-6-phosphate by phosphoglucose isomerase. Glucose-6-phosphate is rearranged into fructose-6-phosphate such that the molecular formula is unchanged. Another isomerase is triose phosphate isomerase. It catalyzes the isomerization of dihydroxyacetone phosphate to glyceraldehyde-3-phosphate. 

Glyceraldehyde phosphate dehydrogenase (GAPDH) is used in the sixth reaction, where G3P is converted to 1,3-bisphosphoglycerate (1,3-BPG). A hydrogen is removed from G3P and added to , yielding NADH. Also, G3P has one phosphate group, while 1,3-BPG has two. The energy released as G3P is oxidized (causing subsequent reduction of ) is highly exergonic. This energy, sometimes referred to as the energy of oxidation, drives the addition of inorganic phosphate onto G3P, yielding the doubly-phosphorylated 1,3-BPG. 

Hexokinase is the first enzyme in the glycolytic pathway and it is responsible for the phosphorylation of glucose to glucose 6-phosphate. The other enzymes catalyze subsequent reactions in glycolysis.

The rate-limiting step of glycolysis is the conversion of glucose-6-phosphate to fructose-6-phosphate. This reaction is catalyzed by the enzyme phosphofructokinase. Hexokinase catalyzes the conversion of glucose to glucose-6-phosphate, pyruvate kinase converts Phosphoenolpyruvate to pyruvate, and lactate dehydrogenase converts pyruvate into lactose.

Glyceraldehyde 3-phosphate dehydrogenase is the only enzyme in glycolysis that carries out a redox reaction. Glyceraldehyde 3-phosphate is oxidized to 1,3-bisphosphoglycerate while  is reduced to . 

The pyruvate dehydrogenase complex essentially carries out a two part reaction: a decarboxylation and an oxidation. All these choices play important roles in the pyruvate dehydrogenase complex. Thiamine pyrophosphate (TPP) is the only choice, however, that is responsible for the decarboxylation step. Lipoamide acts as transporter, transferring the substrate to a distant active site. FAD then reoxidizes lipoamide for the next substrate. CoA is important in producing the substrate.

To see which of the enzymes in these answer choices may by in glycolysis, let's go through each one and look at their function.

Aldolase - This enzyme is indeed involved in glycolysis. It is responsible for the cleavage of fructose-1,6-bisphosphate into two products, glyceraldehyde-3-phosphate and dihydroxyacetone phosphate.

Thiolase - This enzyme catalyzes the the reversible association of two acetyl-CoA molecules into acetoacetyl-CoA. This is an important part of the mevalonate pathway as well as beta oxidation and ketone body synthesis/degradation.

Fructose-1,6-bisphosphatase - This enzyme is important in gluconeogenesis, a metabolic pathway that runs counter to glycolysis. Although many of the enzymes found in glycolysis are also used in gluconeogenesis, this enzyme is one example of an exception because it bypasses one of the irreversible reactions from glycolysis.

Aconitase - This enzyme is found in the citric acid cycle. Its function is to convert citrate into its isomer, isocitrate.

Hexokinase initiates the first step of glycolysis, which we know is the series of reactions by which glucose is processed to enter the citric acid cycle, and generate energy for the cell. So, in the case of glycolysis, glucose is the substrate of hexokinase. Based upon the name of the enzyme, we can infer that it phosphorylates a six-carbon molecule (which glucose is). By knowing the substrate is glucose, the correct product is glucose-6-phosphate, since its name indicates phosphorylation (addition of a phosphate group) to one of its carbons. Glycogen, fructose, and ATP are not involved in this first step of glycolysis. 

Hexokinase, pyruvate kinase, and PFK are regulatory enzymes in glycolysis, but PFK catalyzes the rate-limiting step (the phosphorylation of fructose-6-phosphate). Citrate synthase and isocitrate dehydrogenase are involved in the Krebs cycle, not glycolysis.