The rate of biomass production is called productivity. It is expresse…

The correct answer is Option (3) → (kcal m⁻²) yr⁻¹

Productivity is a rate: the amount of biomass or energy made per unit area (per square metre, m⁻²) per unit time (per year, yr⁻¹). Energy is counted in kilocalories (kcal).

Option (1) (kcal m⁻¹) yr⁻¹ — Incorrect. m⁻¹ is per metre, a length, not per unit area.

Option (2) (kcal m⁻²) yr⁻² — Incorrect. yr⁻² would mean per year per year; a rate is per year once.

Option (3) (kcal m⁻²) yr⁻¹ — Correct. Energy per square metre per year.

Option (4) (kcal m⁻¹) yr⁻² — Incorrect. Both powers are wrong: it is neither per unit area nor per year.

Note: A similar question was also asked in CUET (UG) 2026 on 15-05-2026 (Slot 1), and in CUET (UG) 2025 on 30-05-2025 (Slot 1) and on 15-05-2025 (Slot 1).

NCERT Extract:
Productivity – “A constant input of solar energy is the basic requirement for any ecosystem to function and sustain. Primary production is defined as the amount of biomass or organic matter produced per unit area over a time period by plants during photosynthesis. It is expressed in terms of weight (g m^–2) or energy (kcal m^–2). The rate of biomass production is called productivity. It is expressed in terms of gm^–2 yr^–1 or (kcal m^–2) yr^–1 to compare the productivity of different ecosystems.”