JEE Chemistry 2025 Question with Solution

Given: Two statements about the relation between X-ray emission frequency and atomic properties are to be checked.

Find: Which statement is correct using Moseley's law.

Moseley's law states:

$$\sqrt{\nu} = a(Z-b)$$

where $\nu$ is the frequency of characteristic X-rays, $Z$ is the atomic number, and $a,b$ are constants.

So, a plot of $\sqrt{\nu}$ versus atomic number $Z$ is a straight line.

Therefore, Statement I is false because frequency of X-rays is not linearly related to atomic mass.

Also, Statement II is false because the linear relation is between $\sqrt{\nu}$ and atomic number, not between $\nu$ and atomic number.

Therefore, both Statement I and Statement II are false. The correct option is C.

Given:

1. Statement I claims that a plot of $\nu$ versus atomic mass is a straight line.
2. Statement II claims that a plot of $\nu$ versus atomic number is a straight line.

Find: Truth value of both statements.

For characteristic X-rays, the relevant relation is Moseley's law:

$$\sqrt{\nu} = a(Z-b)$$

This means:

• $\sqrt{\nu}$ varies linearly with atomic number.
• $\nu$ itself does not vary linearly with atomic number.
• There is no straight-line relation with atomic mass.

Hence:

• Statement I is false.
• Statement II is false.

Therefore, the correct option is C, that is, both statements are false.