Q.

Drug X becomes ineffective after 50% decomposition. The original concentration of drug in a bottle was 16 mg/mL which becomes 4 mg/mL in 12 months. The expiry time of the drug in months is _______.

Assume that the decomposition of the drug follows first order kinetics.             [2025]
 

1 6  
2 12  
3 2  
4 3  

Ans.

(1)

After every t1/2, concentration of reactants in a first order reaction becomes half. 

16mgmL6 months8mgmL6 months4mgmL

So in 6 months, the drug becomes ineffective.