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Assertion: The crystal structure of calcium fluoride (CaF_2) is a face-centered cubic lattice.

Reasoning: In CaF_2, eachCa^{2+} ion is surrounded by 8 F-ions and each F^- ion is surrounded by 4 Ca^{2+} ions.

 

Option: 1

Both assertion and reasoning are true and the reasoning is the correct explanation of the assertion.

 


Option: 2

Both assertion and reasoning are true, but the reasoning is NOT the correct explanation of the assertion.


Option: 3

Assertion is true, but the reasoning is false.


Option: 4

Assertion is false, but the reasoning is true.


Answers (1)

best_answer

The assertion that the crystal structure of calcium fluoride (CaF_2) is a face-centered cubic lattice is true. CaF_2crystallizes in a cubic crystal structure, known as the fluorite structure. The fluorite structure belongs to theF_m-3_m space group and is characterised by face-centered cubic packing of the anions (F^-) with the cations (Ca^{2+}) occupying the tetrahedral interstices. Each Ca^{2+} ion is surrounded by8 F^- ions and eachF^-ion is surrounded by 4 Ca^{2+}ions.

The reasoning provided for the assertion is also true. In the fluorite structure, each Ca^{2+}ion is coordinated by 8 F- ions, which are located at the corners of a cube surrounding the Ca^{2+}ion. EachF^-ion is coordinated by 4 Ca^{2+}ions, which are located at the vertices of a tetrahedron surrounding theF^- ion. This coordination pattern ensures that each ion is in electrostatic equilibrium with its nearest neighbours, and the crystal structure is energetically favourable.

Therefore, option a) "Both assertion and reasoning are true and the reasoning is the correct explanation of the assertion" is the correct answer.

Posted by

sudhir.kumar

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