ZnS, CdSe and HgTe are examples of groups 12 – 16 compounds.

Hexagonal crystal system is present in Graphite, ZnO and CdS.

Corundum structure: Anions form hexagonal closest packing and cations are present in 2 / 3 of the octahedral holes. The general formula of the compound is M₂O₃. Examples: Fe₂O₃, Al₂O₃, Cr₂O₃, etc.

The ccp lattice is formed by the element N. The number of octahedral voids generated would be equal to the number of atoms of Y present in it. Since all the octahedral voids are occupied by the atoms of M, so their number would also be equal to that of the element N. Thus, the atoms of elements M and N are present in equal numbers or 1 : 1 ratio. Therefore, the formula of the compound is MN.

Germanium doped with phosphorus is an example of n-type semiconductor. Silicon and germanium are group 14 elements having four valence electrons. In their crystals, each atom forms four covalent bonds with its neighbours. When doped with a group 15 element like P or As, which contains five valence electrons, they occupy some of the lattice sites in silicon or germanium crystal. Four out of five electrons are used in the formation of four covalent bonds with the four neighbouring silicon atoms. The fifth electron is extra and becomes delocalised. These delocalised electrons increase the conductivity of doped silicon or germanium. Here the increase in conductivity is due to the negatively charged electron. Hence, silicon or germanium doped with electron-rich impurity are called n-type semiconductor.

The number of tetrahedral voids formed is equal to twice the number of atoms of element Q and only 2 / 3^rd of these are occupied by the atoms of element P. Hence, the ratio of the number of atoms of P and Q is 2 × (2 / 3) : 1 or 4 : 3 and the formula of the compound is P₄Q₃.

Volume of the unit cell = (210 pm)³= (210 ×10^-12 m)³ = (210 × 10^-10 cm)³ = 9.94 × 10^-24 cm³ Volume of 208 g of the element = mass / density = 210 g / 4.2 g cm^-3 = 50 cm³ Number of unit cells in this volume = 50 cm³ / 9.94 x 10^-24 cm³ = 5.03 x 10²⁴ Since each bcc cubic unit cell contains 2 atoms, so the total number of atoms in 210 g of the element = 2 (atoms / unit cell) × 5.03 x 10²⁴ unit cells = 10.06×10²⁴ atoms

In fluorite structure, cations are arranged into cubic close packing and the anions occupy all the tetrahedral voids.

Rock-salt structure: Anions occupy the lattice points of expanded face centred cubic lattice and the cations occupy all the octahedral holes. The limiting radius ratio is in between 0.414 and 0.732. The co-ordination numbers for both cation and anion is 6 : 6. The general formula of ionic compounds having this structure is AB. Examples: NaCl, KCl, MgO, CaO etc.

Both copper and nickel crystallise in face centered cubic (fcc) arrangement.

CaF₂ and PbCl₂ crystallise in fluorite structure.

SnO₂ crystallises to form tetragonal lattice structure. BaSO₄ crystallises to form orthorhombic lattice structure. ZnO crystallises to form hexagonal lattice structure. CaCO₃ crystallises to form trigonal lattice structure.

Rock-salt structure: Anions occupy the lattice points of expanded face centred cubic lattice and cations occupy all the octahedral holes. The limiting radius ratio is in between 0.414 and 0.732. The coordination numbers of cation and anion are (6 : 6). The general formula of ionic compounds having this structure is AB. Examples: NaCl, KCl, MgO, CaO, etc. Fluorite structure: Cations are arranged into cubic close packing and anions occupy all the tetrahedral voids. Thus, there are four cations and eight anions per unit cell. The formula of ionic compound having this structure is A₄B₈ or AB₂. The coordination numbers of cation and anion are (8 : 4). Examples: CaF₂, ZrO₂, ThO₂, BaF₂, BaCl₂, SrCl₂, PbCl₂, etc. Anti-fluorite structure: Anions are arranged in cubic closest packing and cations occupy all the tetrahedral voids. There are four anions and eight cations per unit cell of this structure and hence, the general formula of an ionic compound is A₈B₄ or A₂B. The ideal radius ratio is between 0.225 - 0.414 (but this ratio is not always maintained). The coordination numbers of cation and anion are (4 : 8). Examples: Na₂O, K₂O, Li₂O, Rb₂O, K₂S, Cl₂O, Na₂S, etc. Zinc-blende or sphalerite structure: Anions occupy the face centred cubic lattice points and cations occupy half of the tetrahedral holes. The ideal radius ratio is in between 0.225 and 0.414. There are four anions and four cations in the unit cell. Therefore, the formula is A₄B₄ or AB. The coordination numbers of cation and anion are (4 : 4). Examples: ZnS, BeO, etc.

Packing efficiency in hcp lattice is 74%. Packing efficiency of bcc lattice structure is 68%.

Correct answer. CCl₄ is an example of molecular solid. CaF₂ is an example of ionic solid. Cu is an example of metallic solid. AlN is an example of network solid.