Which unit can be used to express the rate of a reaction?

mL / s

mL / g

g / mL

mL / mol

s / mL

The rate of reaction may be expressed as a unit of quantity divided by a unit of time. The only expression that has a quantity divided by time is the first one mL / s (i. e. milliliter per second), so the answer is the first option, mL/s.