Question

A first order reaction is 75% completed in 6000 s. What is its half life period at the same temperature? ________.

• A. 15 min
• B. 25 min
• C. 75 min
• D. 50 min
• E. 60 min

Hint:

$t_{75\%} = 2 t_{1/2}$; $t_{87.5\%} = 3 t_{1/2}$; $t_{93.75\%} = 4 t_{1/2}$.

Answer 1

The Correct Option is D

Step 1: Concept
For a first-order reaction, the time required for 75% completion ($t_{75\%}$) is exactly twice the half-life ($t_{1/2}$).

Step 2: Meaning
$t_{75\%} = 2 \times t_{1/2}$.

Step 3: Analysis
$6000 \text{ s} = 2 \times t_{1/2} \implies t_{1/2} = 3000 \text{ s}$.

Step 4: Conclusion
$t_{1/2} = \frac{3000}{60} = 50 \text{ min}$. Final Answer: (D)