Discussion
According to Weiss molecular theory near the critical point the isothermal susceptibility of the magnetic system behaves as :
Answer: B
Near the critical point \(\chi_{T} \propto |T - T_{C}|^{-1}\).
In Weiss's molecular field theory each spin feels the applied field plus an internal field proportional to the magnetisation. Solving self-consistently above \(T_{C}\) gives the Curie-Weiss law:
\[ \chi = \frac{C}{T - T_{C}} \]
So the susceptibility diverges with critical exponent \(\gamma = 1\), the mean-field value. The exponent 1/2 belongs to the magnetisation below \(T_{C}\) (\(M \propto (T_{C} - T)^{1/2}\), \(\beta = 1/2\)), not the susceptibility, and a positive power would make \(\chi\) vanish at the critical point instead of diverging.
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