Question

Assertion :A tetrahedral void is surrounded by four spheres and an octahedral void is surrounded by six spheres. Reason: The number of tetrahedral voids is double the number of close packed spheres and number of octahedral voids is equal to number of close packed spheres.

• A. Both Assertion and Reason are correct and Reason is the correct explanation for Assertion
• B. Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion
• C. Assertion is correct but Reason is incorrect
• D. Both Assertion and Reason are incorrect

Answer 1

The correct option is B Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion

The tetrahedral void is formed when one sphere (atom) is placed in a depression formed by three spheres (atoms). It can be thought of as a vacant space among $4$ constituent particles having a tetrahedral arrangement in the crystal lattice.

So, the coordination number of this void is $4$. There are two tetrahedral voids per sphere (atom) in the crystal lattice (one on each side), i.e if $N$ atoms are there is closed packing structure, $2N$ will be the number of tetrahedral voids.

The octahedral void is formed when the equilateral triangle is formed by $3$ closed pack structure covers another set of three spheres in opposite directions. It can be thought as of vacant space at the center of six spheres placed octahedrally.

So, we have one octahedra void per sphere in the crystal lattice and their number is same as the number of close-packed spheres