Question:

Given below are two statements: one is labelled as Assertion $A$ and the other is labelled as Reason $R$
Assertion (A): The nuclear density of nuclides ${ }_5^{10} B ,{ }_3^6 Li ,{ }_{26}^{56} Fe ,{ }_{10}^{20} Ne$ and ${ }_{83}^{209} Bi$ can be arranged as $\rho_{ Bi }^N>\rho_{ Fe }^N>\rho_{ Ne }^N>\rho_{ B }^N>\rho_{ Li }^N$.
Reason R: The radius $R$ of nucleus is related to its mass number $A$ as $R=R_0 A^{1 / 3}$, where $R_0$ is a constant.
In the light of the above statements, choose the correct answer from the options given below

Updated On: Mar 19, 2025
  • Both $A$ and $R$ are true and $R$ is the correct explanation of $A$
  • $A$ is false but $R$ is true
  • Both $A$ and $R$ are true but $R$ is NOT the correct explanation of $A$
  • A is true but $R$ is false
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The Correct Option is B

Solution and Explanation

Assertion A states that the nuclear densities follow the order: ρ Bi > ρ Fe > ρ Ne > ρ B > ρ Li.
Reason R states that the radius of a nucleus is related to its mass number A as R = \(R_0 A^{\frac {1}{3}}\), where R0 is a constant.
These two statements do not have a direct connection. The arrangement of nuclear densities does not directly relate to the formula for nuclear radius.
Nuclear density is independent of A.

So, the correct answer is (B): A is false but R is true.

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Concepts Used:

Nuclei

In the year 1911, Rutherford discovered the atomic nucleus along with his associates. It is already known that every atom is manufactured of positive charge and mass in the form of a nucleus that is concentrated at the center of the atom. More than 99.9% of the mass of an atom is located in the nucleus. Additionally, the size of the atom is of the order of 10-10 m and that of the nucleus is of the order of 10-15 m.

Read More: Nuclei

Following are the terms related to nucleus:

  1. Atomic Number
  2. Mass Number
  3. Nuclear Size
  4. Nuclear Density
  5. Atomic Mass Unit