Question

A reaction is $50\%$ complete in $2$ hours and $75\%$ complete in $4$ hours. The order of reaction is?

• A. $0$
• B. $1$
• C. $2$
• D. $3$

Answer 1

The correct option is B $1$

The reaction goes to $50$% completion in first $2$ hours. If the initial concentration is $A$, it becomes $A/2$ in $2$ hours.

Then, in the next $2$ hours, it comes $A/4$ from $A/2$. This means it again reduced by half in $2$ hours.

This means the half-life of the reaction is $2$ hours which is constant. Half-life is constant in the first order reaction. Hence, the order of the reaction is $1$.