Answer:
The conversion of glucose to glucose 6‑phosphate;
The formation of fructose 1,6‑bisphosphate from fructose 6‑phosphate;
The formation of pyruvate and ATP from phosphoenolpyruvate and ADP;
The formation of 3‑phosphoglycerate and ATP from 1,3‑bisphosphoglycerate and ADP
Explanation:
All the above mentioned reactions of glycolysis are irreversible. The reason why these are irreversible is because they are involved in either the phosphorylation of the target molecule or removal of the phosphate group from the target molecule. In rest of the reactions of glycolysis either isomerization or rearrangement of carbon atoms is occurring which does not require much energy so the reactions are reversible.
During phosphorylation, phosphate group forms a covalent bond (very strong bond) with the target molecule that is why it requires a lot of energy to break this bond so as to regenerate the reactants again making the reverse reaction impossible.
Reversible reactions on the other hand require weak bonding at the point of interaction so that it could be easier to regenerate the reactants from the product.