Following plots show magnetization (M) vs magnetizing field (H) and magnetic susceptibility (χ) vs temperature (T) graph :
Which of the following combination will be represented by a diamagnetic material?

Solution

Physics sir · 3 steps

A diamagnet pushes back: M opposes H, so χ is negative, and it does not care about temperature.

1. Sign of magnetization. In a diamagnetic material the induced magnetization points opposite to the applied field. So M = χ H with χ < 0, and the M vs H graph is a straight line through the origin with a negative slope.
2. Temperature dependence. Diamagnetism comes from orbital motion responding to the field, not from aligning permanent dipoles. Thermal agitation has nothing to disturb, so χ stays negative and constant as T changes.

   Graph	What it shows	Material
   (a)	M vs H line with negative slope, so χ < 0	diamagnetic
   (b)	M vs H line with positive slope, so χ > 0	paramagnetic
   (c)	χ negative and independent of T	diamagnetic
   (d)	χ positive and falling as 1/T	paramagnetic (Curie law)

3. So. The diamagnetic pair is graphs (a) and (c), which is option (a).

The idea to keep. Read the sign first: negative χ means diamagnetic. Then read the trend: only paramagnets follow Curie's law χ ∝ 1/T; a diamagnet's χ is flat in temperature.

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