Question

Assertion (A): In Rutherford’s alpha particle scattering experiment, the presence of only few alpha particles at angle of scattering \( \pi \) led him to the discovery of the nucleus.
Reason (R): The size of the nucleus is approximately \( 10^{-5} \) times the size of an atom and therefore only few alpha particles are rebounded.

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

Hint:

In Rutherford’s alpha particle scattering experiment, the deflection of alpha particles at large angles provided evidence of the existence of a dense nucleus. The small size of the nucleus explains why only a few alpha particles were deflected significantly.

Answer 1

The Correct Option is A

In Rutherford's alpha particle scattering experiment, alpha particles were directed at a thin gold foil, and their scattering patterns were observed. This experiment was instrumental in the discovery of the atomic nucleus.

Assertion (A): The observation that only a small fraction of alpha particles were deflected by large angles, approaching \( \pi \), was crucial. This indicated the existence of a small, positively charged nucleus that repelled these alpha particles. This inference is logical because if the positive charge were distributed over a larger volume, a greater number of particles would have been deflected at smaller angles, rather than only a few at large angles.

Reason (R): The nucleus is exceedingly small relative to the atom, approximately \( 10^{-5} \) times the atom's total size. Consequently, most alpha particles traversed the atom without significant deflection, with only occasional particles being deflected by the dense, centrally positioned nucleus.

The presence of the nucleus is the cause of these deflections, confirming both the assertion and the reason as true. Furthermore, the reason directly elucidates the assertion's correctness by explaining that the nucleus's small size accounts for the infrequent observation of large-angle scatterings.

Conclusion: Both Assertion (A) and Reason (R) are accurate, and Reason (R) provides the correct explanation for Assertion (A).