27. The matrix corresponding to a 1bar (Place bar symbol over 1)-fold rotation
along z-axis using orthogonal system is:
(a)
À1 0
0
0 À1 0
0
0 À1
0
@
1
A
(b)
0 À1 0
1 0 0
0 0 1
0
@
1
A
(c)
0 1 0
À1 0 0
0 0 À1
0
@
1
A
(d)
1 0 0
0 1 0
0 0 1
0
@
1
A
28. When a mirror plane is combined with a 2-fold axis (perpendicular to mirror)
produces the point group:
(a) 2
(b) 2/m
(c) 3m
(d) 3/m
29. Two mutually perpendicular 2-fold axes produce:
(a) 4-fold
(b) 4-fold
(c) 2-fold
(d) 2-fold
30. A combination of 2-fold and mirror produces a mirror line of second from away
from the first:
(a) 30°
(b) 45°
(c) 60°
(d) 90°
31. A combination of 4-fold and mirror produces a pair of mirror lines of second
from away from the first:
(a) 30°
(b) 45°
(c) 60°
(d) 90°
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6 Unit Cell Symmeteries and Their Representations