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GATE 2024 MT – Question 44

Materials Science and Non-Metallic Materials · Crystal structures and bonding · 2 marks · Multiple choice

Match the entries in Column I with stacking sequences of close-packed planes in Column II.

Column I:

P. FCC structure

Q. Intrinsic stacking fault in FCC

R. Across an annealing twin boundary in FCC

S. HCP structure

Column II:

1. ABCABABC

2. ABABABAB

3. ABCABCABC

4. ABCABCACBACBA

  1. P – 1, Q – 3, R – 4, S – 2
  2. P – 2, Q – 3, R – 1, S – 4
  3. P – 3, Q – 1, R – 4, S – 2
  4. P – 2, Q – 4, R – 1, S – 3

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Correct answer: (C) P – 3, Q – 1, R – 4, S – 2

Explanation

Perfect FCC repeats ABC (P3); deleting a layer produces the intrinsic-fault sequence ABCABABC (Q1).

An annealing twin reverses the stacking sense across the boundary (R4).

HCP repeats AB (S2).

Thus **P3,Q1,R4,S2, C**.