Slope of concentration-time graph for reactant and product represents which rate of reaction?

Instantaneous rate of reaction

The instantaneous rate is obtained when a very small change in concentration (dC) is divided by very small time interval (dt).

Instantaneous rate, rinst = -\(\frac{d[R]}{dt}\) = - slope (for reactant)

                                    = \(\frac{d[P]}{dt}\) = + slope (for product)