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Atoms — Physics STD 12 Science — Question

Rajasthan BoardEnglish MediumSTD 12 SciencePhysicsAtoms1 Mark
Question
For question two statements are given-one labelled Assertion (A) and the other labelled Reason (R). Select the correct answer to these questions from the codes (a), (b), (c) and (d) as given below.
  1. Both A and R are true, and R is the correct explanation of A.
  2. Both A and R are true, but R is NOT the correct explanation of A.
  3. A is true, but R is false.
  4. A is false and R is also false.
Assertion (A): For the scattering of $\alpha$-partides at a large angles, only the nucleus of the atom is responsible.
Reason (R): Nucleus is very heavy in comparison to electrons.
✓

Answer

  1. Both A and R are true, and R is the correct explanation of A.
Explanation:
We know that an electron is very light particle as compared to an $\alpha$-particle. Hence, electron cannot scatter the $\alpha$-particle at large angles, according to law of conservation of momentum. On the other hand, mass of nucleus is comparable with the mass of $\alpha$-particle, hence only the nucleus of atom is responsible for scattering of $\alpha$-particles.

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