Here's why:

* Pyruvate: C₃H₄O₃ (3 carbons, 4 hydrogens, 3 oxygens)

* Lactate: C₃H₆O₃ (3 carbons, 6 hydrogens, 3 oxygens)

Key difference: Lactate has two more hydrogen atoms than pyruvate.

The conversion of pyruvate to lactate involves the addition of two hydrogen atoms from NADH, which is reduced to NAD+.