Select the correct statement(s):
A. Rate constants are never negative.
B. Partial orders are never negative.
C. Molecularity and order of reaction both are equal for elementary reactions.
D. Order of reaction remains unchanged during the reaction.

Hint: We know that the rate of reaction is the speed at which reaction proceeds. It is generally measured as change in the concentration of products or reactants or the concentration of products divided by the time taken for it.

Complete step by step answer:
The following are the four factors that influence the rate of reaction, nature of reactants, catalyst, Temperature, concentration of the reaction.
> Here now we discussed the rate constant, it cannot be negative because it measures how fast the concentration changes over time so it cannot be a negative value. However, the rate of disappearance can be negative.
> And we know that a reaction can have a negative partial order with respect to substance. For example the conversion of ozone to oxygen, oxygen has negative order with respect to oxygen. Which means partial orders can be negative.
> We define the molecularity as the number of molecules taking part in a chemical reaction. It can have value one two and occasionally three. It cannot be negative, zero or fractional. It also cannot be greater than three. This is due to the fact that more than three molecules cannot collide with each other simultaneously. Even if they collide these collisions are not effective collisions which lead to the formation of a successful product. Therefore, molecularity is applicable only to an elementary reaction. It can be obtained theoretically. Molecularity and order of reaction both are equal for elementary reactions because these are single step reactions.
> If we define order of reaction, it defines as the sum of powers of the concentration of the reacting species in the rate expression. It is an experimental concept and it is not necessarily related to the stoichiometric coefficients. It can have fractional value and need not to be an integer. It remains constant during the reaction.

Therefore, correct answers are (A) (C) and (D).

Note: The order of reaction is related to the concentration of the species that determine the rate determined step. Many reactions go through the different transition states hence for many reactions, the reaction orders are not necessarily equal to the stoichiometric coefficients.