Answer:
a. The concentration of β-galactosidase
Explanation:
β-Galactosidase is an enzyme that hydrolyzes ß-D-galactosides like lactose to glucose and galactose.
It also cleaves o-nitrophenyl-β-D-galactoside (ONPG) to yield galactose and o-nitrophenol, which is yellow, and can be measured by its absorption at 420 nm.
If the concentration of ONPG is greater than that of β-galactosidase, the concentration of o-nitrophenol produced is proportional to the concentration of the enzyme.
