The given graph is for :

The correct answer is Option (2) → Instantaneous rate of reaction

The graph plots the molar concentration of a reactant against time. At the point y on the curve a tangent is drawn (the dashed line CB). The slope of this tangent gives the rate at that one instant:

    r_inst = −d[R]/dt = −(slope of the tangent at y)

This is the instantaneous rate, the average rate taken over an infinitely small time interval.

Why the other options are incorrect

• Option (1) Average rate of reaction — Incorrect. The average rate is −Δ[R]/Δt between two points on the curve (a chord, not a tangent at one point).

• Option (3) Initial rate for product — Incorrect. The curve falls with time, so it is for a reactant, and the tangent is drawn at y, not at t = 0.

• Option (4) Final rate for reactant — Incorrect. The tangent is at an intermediate point y, not at the end of the reaction, where the slope would be almost zero.

NCERT (2026-27 edition):
Rate of a Chemical Reaction – “… It can be determined graphically by drawing a tangent at time t on either of the curves for concentration of R and P vs time t and calculating its slope (Fig. 3.1). … A tangent is drawn that touches the curve at t = 600 s (Fig. 3.2). The slope of this tangent gives the instantaneous rate.”