Question

Assertion (A) : A free neutron is not a stable particle.

Reason (R) : It decays into a proton and an electron.

• A. Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A).
• B. Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of the Assertion (A).
• C. Assertion (A) is true, but Reason (R) is false.
• D. Both Assertion (A) and Reason (R) are false.

Hint:

A free neutron decays (n to p + e + antineutrino), and that decay is why it is unstable.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
A neutron is stable only inside a nucleus. Outside the nucleus, a free neutron decays by beta decay, with a mean life of about 15 minutes.

Step 2: Check the Assertion:
A free neutron is heavier than a proton plus an electron. It therefore changes into lighter particles and releases energy.
So a free neutron is not stable. The Assertion is TRUE.

Step 3: Check the Reason:
The decay is \(n \to p + e^- + \bar{\nu}\). The neutron decays into a proton and an electron (plus an antineutrino that carries some energy).
The Reason names the main charged products, so it is TRUE.

Step 4: Does R explain A?
Yes. The decay of the neutron into other particles is exactly why it is unstable. The Reason describes the process behind the Assertion.

Step 5: Eliminate the wrong options:
(B) says R does not explain A, but the decay is the cause of the instability.
(C) says R is false, but a free neutron really decays into a proton and an electron.
(D) says both are false, which is wrong.

Final Answer:
Both are true and R explains A. This is option (A). \[ \boxed{\text{Option (A)}} \]