Assertion : Conversion of PEP into pyruvic acid is a substrate level phosphorylation reaction.

Reason: ATP is formed directly when ADP accepts the released phosphate from the substrate PEP.

Both (A) and (R) are correct (R) explains (A).

Assertion is correct. Substrate-level phosphorylation is a type of ATP synthesis where a high-energy phosphate group is directly transferred from a phosphorylated substrate to ADP, forming ATP. Conversion of PEP into pyruvic acid is a substrate level phosphorylation reaction.

Reason is correct. The formation of pyruvate from PEP during glycolysis does release a phosphate group, which is used to directly synthesize ATP through substrate-level phosphorylation.