Question

Study the following graphs and choose the correct option

(i) in fig.$ a, A$ represents average rate and $B$ represents instantaneous rate
(ii) in fig. $b, D$ represents average rate and $C$ represents instantaneous rate
(iii) fig. $a, A$ represents instantaneous rate and $B$ represents average rate
(iv) fig. $b, C$ represents average rate and $D$ represents instantaneous rate

• A. (i) and (ii) are correct
• B. (ii) and (iv) are correct
• C. (i) and (iv) are correct
• D. (ii) and (iii) are correct

Answer 1

Answer: (A)

Average rate depends upon the change in concentration of reactants or products and the time taken for that change to occur. Average rate cannot be used to predict the rate of a reaction at a particular instant as it would be constant for the time interval for which it is calculated. So, to express the rate at a particular moment of time, we determine the instantaneous rate. It is obtained when we consider the average rate at the smallest time interval say $d t$ (i.e. when it approaches zero).