A reaction of first-order completed `90%` in 90 minutes, hence, it is completed `50%` in approximately :

Explanation

To solve the problem, we need to determine the time it takes for a first-order reaction to complete 50% of the reaction given that it completes 90% in 90 minutes. Here’s a step-by-step solution:

### Step 1: Understand the First-Order Reaction
For a first-order reaction, the rate constant \( k \) can be calculated using the formula:
\[ k = \frac{2.303}{t} \log \left( \frac{A}{A - x} \right) \]
where:
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