Secondary productivity is:

The correct answer is Option (3) → Rate of formation of new organic matter by consumers.

Option (1) Measured by organic matter produced. — Incorrect. It is a rate, not just the organic matter made.

Option (2) Rate of formation of new organic matter by producers. — Incorrect. New organic matter made by producers (plants) in photosynthesis is primary productivity. Secondary productivity is measured at the level of the consumers.

Option (3) Rate of formation of new organic matter by consumers. — Correct. Consumers build their own body matter from the food they eat; the rate at which they do so is secondary productivity. Producers make organic matter first, by photosynthesis, which is primary productivity.

Option (4) Always greater than primary productivity. — Incorrect. Consumers get all their food from producers, and only a part of it becomes their body matter. So secondary productivity is less, not greater, than primary productivity.

NCERT Extract:
Productivity – “… Gross primary productivity minus respiration losses (R), is the net primary productivity (NPP). GPP – R = NPP Net primary productivity is the available biomass for the consumption to heterotrophs (herbiviores and decomposers). Secondary productivity is defined as the rate of formation of new organic matter by consumers.”