Assertion: $6 : 6$ co-ordination at normal temperature and pressure changes to $8 : 8$ co-ordination at high pressure.
Reason: Pressure influences the structure of solids.

Both Assertion and Reason are correct and Assertion is the correct explanation of Reason.

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Both Assertion and Reason are correct but Reason is not the correct explanation of Assertion.

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Assertion is correct but Reason is wrong.

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Assertion is wrong but Reason is correct.

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Solution

The correct option is A Both Assertion and Reason are correct and Assertion is the correct explanation of Reason.
As pressure increases the close packed structure changes to a less packed structure.For example- NaCl (6:6) structure to CsCl (8:8) structure.

Option A-Both Assertion and Reason are correct and Assertion is the correct explanation of Reason.

$Explanation :$
As we know that $α$ Iron has a BCC structure and γ-Fe has a FCC structure (refer- Fe-C phase diagram).
As the pressure is increased, the α-Fe $\to$ γ-Fe transition temperature is lowered, whereas γ-Fe $\to$ δ Fe transition temperature is raised. This is true to Le Chateliers principle. As γ-Fe (FCC) is a close-packed structure, it resists the pressure more than α-Fe, or δ-Fe (BCC) which are more open structures (less densely packed), and that is why the area of stabilisation of γ-Fe increases with the increase of pressure. Thus, a FCC changes to BCC structure.

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Similar questions

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6 : 6

co-ordination at normal temperature and pressure changes to

8 : 8

co-ordination at high pressure. Reason: Pressure influences the structure of solids.

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Assertion: 6:6 co-ordination at normal temperature and pressure changes to 8:8 co-ordination at high pressure.Reason: Pressure influences the structure of solids.

Assertion: $6 : 6$ co-ordination at normal temperature and pressure changes to $8 : 8$ co-ordination at high pressure.
Reason: Pressure influences the structure of solids.