A in the following graph is:

The correct answer is Option (2) → Most probable kinetic energy

At a given temperature the molecules of a gas have a spread of kinetic energies. The peak of the Maxwell–Boltzmann curve is the energy held by the largest fraction of molecules, the most probable kinetic energy. The activation energy lies far out in the right-hand tail, where only a small fraction of molecules reach it.

Why the other options are incorrect

• Option (1) Threshold energy — Incorrect. The threshold energy is the least energy a colliding molecule must have for the reaction to occur. Only a small fraction of molecules have this much energy, so it is marked far out in the right-hand tail of the curve, not at the peak.

• Option (3) Effective collision — Incorrect. An effective collision is a collision with enough energy and the proper orientation to form products. It is an event, not an energy value, so it cannot be a point on the kinetic-energy axis of the curve.

• Option (4) Temperature coefficient — Incorrect. The temperature coefficient is the ratio of the rate constants at two temperatures 10 K apart (about 2 to 3 for many reactions). It is a ratio, not a point on the energy distribution curve.

NCERT (2026-27 edition):
Temperature Dependence of the Rate of a Reaction – …

Note: The same/similar question has been asked in different years by NTA as per the details given below: