AIIMS 2018 Chemistry Dielectric Constant MCQ Question

The electrostatic force of attraction between Na⁺ and Cl⁻ is described by Coulomb's law, which states that the force $F$ is inversely proportional to the square of the distance between the charges and directly proportional to the product of the charges. In a medium like water (H₂O), the dielectric constant (κ) reduces the effective force between the ions, resulting in the force being reduced by a factor equal to the dielectric constant. Since the dielectric constant of H₂O is 80, the force in water is reduced to $\frac{1}{80}$ of that in air, making option B correct.

Option A is incorrect because it suggests a reduction to $\frac{1}{40}$, which does not reflect the actual dielectric constant. Option C incorrectly states that the force will increase, which contradicts the effect of the dielectric medium. Option D is also incorrect as it implies no change in the force, ignoring the significant impact of the dielectric constant on electrostatic interactions.