JEE Advanced · 2023 · 04 Jun 2023 · Paper 2 · Solid State

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Atoms of metals , and z form face-centred cubic (fcc) unit cell of edge length , body-centred cubic (bcc) unit cell of edge length , and simple cubic unit cell of edge length , respectively.
If and , then the correct statement (s) is (are)
[Given : , and are molar masses of metals , and z , respectively.
, and are atomic radii of metals x, y, and z, respectively.]
  1. (A)Packing efficiency of unit cell of Packing efficiency of unit cell of Packing efficiency of unit cell of z✓ Correct
  2. (B)✓ Correct
  3. (C)
  4. (D)Density of Density of y✓ Correct

Answer: (A), (B), (D)

Solution

For the three lattice types:
  • FCC: , packing efficiency = 74%
  • BCC: , packing efficiency = 68%
  • Simple cubic: , packing efficiency = 52%

From the given relations:
and

Therefore:
, ,

So

(A) Packing efficiency: FCC > BCC > Simple cubic ✓
(B) ✓
(C) ✗ (actually )

For density:
Using and the edge length relations, density of x > density of y ✓

(D) is correct.

Therefore, (A), (B), and (D) are correct.

JEE Advanced · 2023 · 04 Jun 2023 · Paper 2 · One or more correct options

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