Q127 · CSIR-NET Chemistry, December 2019

Paper: CSIR-NET December 2019 · Subject: Physical Chemistry · Chapter: Group Theory · Topic: Group Theory – General · Marks: 2 · Difficulty: Medium

Given the matrices for $\mathrm{C_3}$ and $\sigma_h$ below
\[ C_{3}=\begin{bmatrix} -\dfrac{1}{2} & -\dfrac{\sqrt{3}}{2} & 0 \\ \dfrac{\sqrt{3}}{2} & -\dfrac{1}{2} & 0 \\ 0 & 0 & 1 \end{bmatrix} \quad \sigma_{h}=\begin{bmatrix} 1 & 0 & 0 \\ 0 & 1 & 0 \\ 0 & 0 & 1 \end{bmatrix} \]
the trace of the matrix representing for $\mathrm{S_3^2}$ is
(a)0
(b)-2
(c)1
(d)-1
Answer
Answer: A ✓ checked by 4AB · confidence high
Explanation
S₃² = C₃²; trace = 1 + 2cos 240° = 0.

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