Problem 56
The number of atoms present in a hexagonal close-packed unit cell is : (a) 4 (b) 6 (c) 8 (d) 12
Problem 60
In the closest packing of atoms, there are: (a) one tetrahedral void and two octahedral voids per atom (b) two tetrahedral voids and one octahedral void per atom (c) two of each tetrahedral and octahedral voids per atom (d) one of each tetrahedral and octahedral void per atom
Problem 62
In which of the following pairs of structures, tetrahedral as well as octahedral holes are found? (a) bce and fcc (b) hcp and simple cubic (c) hcp and ccp (d) bce and hcp
Problem 67
In the closest packing of atoms \(A\) (radius : \(r_{a}\) ), the radius of atom \(B\) that can be fitted into tetrahedral void is: (a) \(0.155 r_{a}\) (b) \(0.225 r_{a}\) (c) \(0.414 r_{a}\) (d) \(0.732 r_{a}\)
Problem 68
In the closest packing of atoms \(A\) (radius : \(r_{a}\) ), the radius of atom \(B\) that can be fitted octahedral void is: (a) \(1.155 r_{a}\) (b) \(0.225 r_{a}\) (c) \(0.414 r_{a}\) (d) \(0.732 r_{a}\)
Problem 69
How many nearest neighbours are there in an atom or ion for an octahedral hole of a closed packed structure? (a) 4 (b) 6 (c) 8 (d) 12
Problem 70
How many "nearest" and "next nearest" neighbours, respectively, does potassium have in bcc lattice ? (a) 8,8 (b) 8,6 (c) 6,8 (d) 6,6
Problem 71
In the closest packing of atoms: (a) the size of tetrahedral void is greater than that of octahedral void (b) the size of tetrahedral void is smaller than that of octahedral void (c) the size of tetrahedral void is equal to that of octahedral void (d) the size of tetrahedral void may be greater or smaller or equal to that of octahedral void depending upon the size of atoms
Problem 73
In the unit cell of \(\mathrm{KCl}(\mathrm{NaCl}\) type \(), \mathrm{Cl}^{-}\) ions constitute ccp and \(\mathrm{K}^{+}\) ions fall into the octahedral holes. These holes are: (a) one at the centre and 6 at the centres of the faces (b) one at the centre and 12 at the centres of the edges (c) 8 at the centres of 8 small cubes forming the unit cell (d) none of these
Problem 76
The CsCl type structure is exhibited by alkali halides only when the radius of the cation is large enough to keep touching its eight nearest neighbour anions. Below what minimum ratio of cation to anion radii \(\left(r^{+} / r^{-}\right)\) this contact is prevented? (a) \(0.225\) (b) \(0.414\) (c) \(0.632\) (d) \(0.732\)
