Answer: Option (a) is the correct answer.
Step-by-step explanation:
Rate of a reaction gets affected by change in temperature as when we decrease the temperature then reactant molecules lose kinetic energy. As a result, there occurs decrease in number of collisions between the molecules.
Hence, rate of reaction also decreases with decrease in temperature.
Whereas when we increase the concentration from 30 mg to 60 mg then there is increase in number of reactant molecules. Therefore, there will be increase in number of collisions between the molecules.
Also, when substance is placed in smaller container then molecules come closer to each other and thus collide more frequently. So, rate of reaction will also increase.
On the other hand, grinding the substance into a powder will also increase the number of reactant particles. Thus, this will also increase the rate of reaction.
Thus, we can conclude that changing the temperature from
to
will decrease the rate of a reaction.