Henry Moseley studied characteristic X-ray spectra of elements. The graph which represents his observation correctly is
Given v= frequency of X-ray emitted
Z = atomic number

Solution

Chemistry ma’am · 3 steps

Moseley's law makes √ν, not ν itself, a straight line against the atomic number Z.

1. Moseley's law. Moseley measured the X-ray frequency ν given out by many elements. He found that the square root of the frequency rises in a straight line with the atomic number Z.

   √ν = a(Z - b)

2. What it means. Here a and b are constants. Squaring gives ν ∝ (Z-b)², so a plot of ν itself against Z is a curve. Only the √ν against Z plot is a straight line. Strictly, that line meets the Z axis at Z = b, a small number, but the straight-line shape is what matters here.

   Option	Plot	Relation it claims	Fits Moseley?
   (a)	ν² against Z	ν ∝ √Z	No
   (b)	√ν against Z	√ν ∝ Z	Yes
   (c)	ν against Z	ν ∝ Z	No, ν grows as Z²
   (d)	√Z against ν	ν ∝ √Z	No

3. So. The straight line of √ν against Z in (b) is Moseley's observation.

The idea to keep. Remember Moseley as √ν ∝ Z. Because ν follows Z and not atomic mass, atomic number became the basis of the modern periodic law.

Answer from the NTA final answer key. Solution by PrepWiser.