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Atoms — Physics STD 12 Science — Question

Rajasthan BoardEnglish MediumSTD 12 SciencePhysicsAtoms1 Mark
MCQ
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.
Assertion $(A):$ The positively charged nucleus of an atom has a radius of almost $10^{-15}m.$
Reason $(R):$ In $\alpha-$particle scattering experiment, the distance of closest approach for $\alpha-$particles is $10^{-15}m.$
  • ✓
    Both $A$ and $R$ are true, and $R$ is the correct explanation of $A.$
  • B
    Both $A$ and $R$ are true, but $R$ is $\text{NOT}$ the correct explanation of $A.$
  • C
    $A$ is true, but $R$ is false.
  • D
    $A$ is false and $R$ is also false.
✓

Answer

Correct option: A.
Both $A$ and $R$ are true, and $R$ is the correct explanation of $A.$
In $\alpha-$particle scattering experiment, Rutherford found a small number of $\alpha-$particles which were scattered back through an angle approaching to $180^\circ.$
This is possible only if the positive charges are concentrated at the centre or nucleus of the atom.

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