In tetragonal crystal system, which of following is not true?

• All axial lengths and all axial angles are equal.

• All three axial lengths are equal.

• All three axial angles are equal.

• Two axial angles are equal but the third is different.

In solid ice, oxygen atom is surrounded

• tetrahedrally by 4 hydrogen atoms

• octahedrally by 2 oxygen and 4 hydrogen atoms

• tetrahedrally by 2 hydrogen and 2 oxygen atoms

• octahedrally by 6 hydrogen atoms

Schottky defect is

• vacancy of ions

• delocalization of ions

• interstitial vacancy of ions

• vacancy of only cations

Assertion : bcc and hcp has same packing efficiency.

Reason : Both have same number of atoms per unit cell and same arrangement.

• If both assertion and reason are true and reason is the correct explanation of assertion.

• If both assertion and reason are true but reason is not the correct explanation of assertion.

• If assertion is true but reason is false.

• If both assertion and reason are false.

Assertion: Due to Frenkel defect, density of the crystalline solid decreases.

Reason : In Frenkel defect, cation or anion leaves the crystal.

• If both assertion and reason are true and reason is the correct explanation of assertion.

• If both assertion and reason are true but reason is not the correct explanation of assertion.

• If assertion is true but reason is false.

• If both assertion and reason are false.

66.

Schottky defect in crystals is observed when

• unequal number cations and anions are missing from the lattice

• equal number of cations and anions are missing from the lattice

• an ion leaves its normal site and occupies an interstitial site

• density of the crystal is increased.

The coordination number in hcp is

• 6

• 12

• 18

• 24

In face centred cubic unit cell edge length is :

• $\frac{4}{\sqrt{3}}$r

• $\frac{4}{\sqrt{2}}$r

• 2r

• $\frac{\sqrt{3}}{2}$r

The incorrect statement among the following is

• C₆₀ is an allotropic form of carbon

• O_3, is an allotropic form of oxygen

• S₈ is only allotropic form of sulphur

• red phosphorus is more stable in air than white phosphorus.

The Ca²⁺ and F^- are located in CaF₂ crystal, respectively at face centred cubic lattice points and in

• tetrahedral voids

• half of tetrahedral voids

• octahedral voids

• half of octahedral voids