Question

What is order of radioactive decay of a substance ?

• A. \(0\)
• B. \(1\)
• C. \(1.5\)
• D. \(2\)

Hint:

Radioactive decay rate is proportional to the number of nuclei present.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Radioactive decay rate depends on how many unstable nuclei remain: \(-\dfrac{dN}{dt} = \lambda N\).

Step 2: Detailed Explanation:
The rate is directly proportional to the first power of \(N\). This is the rate law of a first order reaction.
\[ N = N_0 e^{-\lambda t}, \quad t_{1/2} = \frac{0.693}{\lambda} \]
The half life does not depend on the starting amount, which is a clear sign of first order. Zero, 1.5 and second order laws would give different dependence of rate on \(N\).

Step 3: Final Answer:
Order = 1, option (B).

Final Answer:
Decay rate is proportional to N, so first order. \[ \boxed{\text{(B) }1} \]