Question

The Moseley’s law of the frequency of ${{\text{K}}_\alpha }$ line is $\sqrt {{f_{ha}}} = a\left( {z - 1} \right)$ where $a$ is a constant and $z$ is
A. Mass number
B. Atomic number
C. Neutron number
D. Avogadro’s number

Answer 1

We are given the equation for Moseley’s law of the frequency of ${{\text{K}}_\alpha }$ line. To know which option do $z$ represent, we check each option one by one. We compare the symbolic representation of each option and check what does $z$ represent.

Complete answer:
Given, the Moseley’s law of the frequency of ${{\text{K}}_\alpha }$ line is $\sqrt {{f_{ha}}} = a\left( {z - 1} \right)$ where $a$ is a constant.We are asked what is the term $z$ called.
Let us check each option one by one by comparing their symbolic representation.
Mass number: Mass number is represented as $A$ so, option A is incorrect.
Atomic number: Atomic number is represented as $z$. Therefore, option B is correct.
Neutron number: Neutron number is represented as $n$ , so option C is incorrect.
Avogadro’s number: Avogadro’s number is represented as ${N_A}$ so, option D is incorrect.

Hence, the correct answer is option B.

Note: According to Moseley’s law, the square root of the frequency of the emitted X-rays by an atom is proportional to the atomic number. And it is given as, $\sqrt f = a\left( {Z - b} \right)$where $f$ is the frequency of the emitted X-rays, $a$ and $b$ are constants. Moseley’s law can be used to determine the atomic number of a target material. Moseley’s law was given by the English physicist Henry Moseley. When electrons in the lower orbital of an atom change its orbital, energy is emitted in the form of X-rays. Henry Moseley used this concept to introduce Moseley’s law.