Class 12 NEET Chemistry Chemical Kinetics Questions

Concept:The order of a reaction is identified by which function of concentration gives a straight line against time.A straight line for $[R]$ itself versus time means the rate is independent of concentration, i.e. zero order.Formula / Integrated rate laws:Zero order: $[R] = [R]_0 - kt$, so the plot of $[R]$ vs $t$ is linear with slope $= -k$ (hence $k = -\text{slope}$).First order: $\ln[R] = \ln[R]_0 - kt$, so $\ln[R]$ vs $t$ is linear.Second order: $\frac{1}{[R]} = \frac{1}{[R]_0} + kt$, so $1/[R]$ vs $t$ is linear.Explanation:The given graph is a plot of $[R]$ vs time, and it is a straight line falling with a constant negative slope.A constant negative slope means the rate, $-\frac{d[R]}{dt}$, remains constant throughout the reaction.A constant rate, $\text{rate} = k[R]^0 = k$, is the defining characteristic of a zero-order reaction.The label $k = -\text{slope}$ written on the graph also corresponds exactly to $[R] = [R]_0 - kt$, the zero-order equation.If the reaction were first or second order, $[R]$ vs $t$ would be curved (exponential fall), and only $\ln[R]$ vs $t$ or $1/[R]$ vs $t$ would be linear.Therefore the order of the reaction is $0$.Answer:A. 0 (zero order)