In crystalline solid AB2 has ccp arrangement of A atoms occupying the lattice points. Which of the followingstatements is correct /a)100% octahedral voids are occupied, C.N.of A = 4b)50% tetrahedral voids are occupied, C.N. ofA = 4c)100% octahedral voids are occupied, C.N.of B = 4d)100% tetrahedral voids are occupied, C.N.of B = 4Correct answer is option 'D'. Can you explain this answer?

Question

Answer

Answer

Explanation:

Given:
- Crystalline solid AB2 has a ccp (cubic close-packed) arrangement of A atoms occupying the lattice points.

To determine which statement is correct, we need to understand the arrangement of atoms and voids in a ccp structure.

CCP (cubic close-packed) Structure:
In a ccp structure, the A atoms occupy all the corner positions of the cube and one atom at the center of each face of the cube. This arrangement results in a total of 4 atoms per unit cell. The coordination number (C.N.) of A atoms is determined by the number of atoms they are in direct contact with.

Statement a) 100% octahedral voids are occupied, C.N. of A = 4:
Octahedral voids are formed when two layers of atoms are placed one above the other, with the atoms in the second layer positioned directly above the voids in the first layer. In a ccp structure, each octahedral void is surrounded by 6 A atoms. Therefore, if all the octahedral voids are occupied, it would mean that each A atom is in contact with 6 neighboring A atoms, resulting in a coordination number (C.N.) of 6, not 4. Hence, statement a) is incorrect.

Statement b) 50% tetrahedral voids are occupied, C.N. of A = 4:
Tetrahedral voids are formed when an additional layer of atoms is placed in the depressions between the atoms in the two adjacent layers. In a ccp structure, there are 2 tetrahedral voids per unit cell, which are not occupied by any atoms. Therefore, the A atoms cannot occupy the tetrahedral voids. Hence, statement b) is incorrect.

Statement c) 100% octahedral voids are occupied, C.N. of B = 4:
In the ccp structure, the B atoms are not located at the lattice points but occupy the octahedral voids. Each octahedral void is surrounded by 6 A atoms, resulting in a coordination number (C.N.) of 6 for B atoms. Therefore, statement c) is incorrect.

Statement d) 100% tetrahedral voids are occupied, C.N. of B = 4:
As mentioned earlier, the A atoms cannot occupy the tetrahedral voids in a ccp structure. Therefore, the B atoms occupy the tetrahedral voids. Each tetrahedral void is surrounded by 4 A atoms, resulting in a coordination number (C.N.) of 4 for B atoms. Therefore, statement d) is correct.

In conclusion, the correct statement is d) 100% tetrahedral voids are occupied, C.N. of B = 4.

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