The essential symmetry(ies) for a monoclinic crystal system is/are the presence of:
Show Hint
- one \( C_3 \) axis
- one \( C_2 \) axis
- one \( C_4 \) axis
- one \( C_6 \) axis
The Correct Option is B
Solution and Explanation
The monoclinic crystal system is one of the seven crystal systems in crystallography. It is characterized by:
- Lattice parameters: \( a \neq b \neq c \), with \( \alpha = \gamma = 90^\circ \) and \( \beta \neq 90^\circ \)
- It has a single 2-fold rotation axis (i.e., \( C_2 \)) or a mirror plane perpendicular to the unique axis.
This 2-fold rotational symmetry about one axis is the defining symmetry of monoclinic systems. Other symmetry elements like \( C_3, C_4, \) or \( C_6 \) axes are found in trigonal, tetragonal, or hexagonal systems respectively, and not in monoclinic.
\[ \boxed{\text{The essential symmetry element in a monoclinic crystal system is one } C_2 \text{ axis.}} \]
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