Question

The symmetry elements of a point group are: 3 crystallographic axes of 2-fold symmetry and 3 mirror planes perpendicular to the crystallographic axes. The Hermann – Mauguin notation of the point group is:

• A. 2m2m2m
• B. 2mm
• C. 2/m2/m2/m
• D. 2/m

Hint:

In Hermann-Mauguin notation: "2" denotes 2-fold symmetry, and "m" denotes a mirror plane.

Answer 1

The Correct Option is C

The Hermann-Mauguin notation is used to represent the symmetry of crystal point groups, describing the symmetry operations such as rotations, reflections, and inversions. The notation follows a set of rules to express symmetry elements present in the point group.
Given the symmetry elements in the question: - 3 crystallographic axes of 2-fold symmetry indicate the presence of three symmetry axes that each rotate by 180°. - 3 mirror planes perpendicular to the crystallographic axes suggest the presence of mirror planes that cut through the crystal along axes of symmetry.
The correct notation for this combination of symmetry elements is 2/m2/m, where the 2 denotes the 2-fold symmetry axes, and the m represents the mirror planes. The notation 2/m2/m signifies that there are two perpendicular 2-fold axes and mirror planes for each.
Thus, the correct answer is (C).