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Nuclei — Physics STD 12 Science — Question

Rajasthan BoardEnglish MediumSTD 12 SciencePhysicsNuclei1 Mark
MCQ
For question, 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 $(A)$: Nuclear density is extremely higher than atomic density.
Reason $(R)$: Most of the mass of the atom is concentrated in the nucleus.
  • ✓
    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 $A$.
According to the planetary model of the atom, the mass of the atom is concentrate at the centre, the nucleus. The electrons orbit around the nucleus in circular paths of different radii.
The radius of the outermost orbit gives the size of atom.
The size of the atom is $~ 10^{-10}m$ as compared to the size of the nucleus, $10{-15}^m$. Electrons being extremely light $(m_e = 5.49 \times 10^{-4}u = 9.11 \times 10^{-31}kg)$ as compared to protons and neutrons have a negligible contribution to the weight of the atom.
They mainly increase the volume of the atom.
Therefore, the nuclear density is much higher that the atomic density $\Big(\frac{10^3\text{kg}}{\text{m}^3}\Big)$

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