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GATE 2024 MT – Question 14

Metallurgical Thermodynamics · Solutions and chemical potential · 1 mark · Multiple choice

In an A–B solid solution, the activity and mole fraction of A are $a_A$ and $X_A$. Its activity coefficient is

  1. $a_A/X_A$
  2. $X_A/a_A$
  3. $a_AX_A$
  4. $a_AX_A^2$

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Show answer and explanation

Correct answer: (A) $a_A/X_A$

Explanation

By definition activity relative to the chosen standard state is aA=γAXA.

Therefore **γA=aA/XA, A**.

The coefficient measures departure from ideality; it equals unity for an ideal solution on that standard state.