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GATE 2016 ME (ME2) – Question 58

Engineering Materials · Phase diagrams and heat treatment · 2 marks · Multiple choice

In a binary A–B system, liquid containing 20% A coexists with solid containing 70% A. At overall composition 40% A, the solid fraction is ______.

  1. 0.40
  2. 0.50
  3. 0.60
  4. 0.75

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Show answer and explanation

Correct answer: (A) 0.40

Explanation

Let solid mass fraction be fs. Overall A composition satisfies0.40=0.70fs+0.20(1−fs). Thus0.20=0.50fs and fs=0.40. Therefore **0.40, A**. This is the lever rule between the two coexisting phase compositions.