An optically active drug has one chiral centre and only dextro rotatory isomer is effective. Moreover, it becomes ineffective when its optical activity is reduced to `35%` of original. It was found that mutarotation of this drug was first order reaction with a rate constant of `1 xx 10^(-8) s^(-1)`. Find the expiration time of the drug in years.

Explanation

To solve the problem step by step, we will follow these instructions:

### Step 1: Understand the problem
We have an optically active drug with one chiral center, and only the dextro-rotatory isomer is effective. The drug becomes ineffective when its optical activity is reduced to 35% of its original value. The mutarotation of this drug follows first-order kinetics with a rate constant of \( k = 1 \times 10^{-8} \, \text{s}^{-1} \).

### Step 2: Determine the percentage of optical activity lost
The drug becomes ineffective when its optical activity is reduced to 35%. Therefore, the percentage of optical activity lost is:
\[
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