The correct option is C Both (a) and (b)
Factors affecting rate of reaction:
Effect of Concentration
From law of mass action, we know
Rate of reaction∝Concentration of reactants
Generally, rate of reaction decreases with passage of time ,due to decrease in concentration of reactants.
Effect of temperature:
Most of the chemical reactions are accelerated by increase in temperature.
Effect of catalyst:
Presence of positive catalyst increases the rate of reaction.
Presence of negative catalyst decreases the rate of reaction.
Hence, the correct answer is option (c).