Q. A first order reaction has a specific reaction rate of $10^{-2}$ $sec^{-1}$. How much time will it take for 20 g of the reactant to reduce to 5 g ?
A) 238.6 sec
B) 138.6 sec
C) 346.5 sec
D) 693.0 sec
Explanation
[Solution] Two half-lives: $t = 2 \times 0.693/10^{-2} = 138.6$ s. Answer (2).
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.