Apart from the acoustic modes, 9 optical modes are identified from the measurements of phonon dispersions of a solid with the chemical formula \( A_nB_m \), where \( A \) and \( B \) denote the atomic species, and \( n \) and \( m \) are integers. Which of the following combinations of \( n \) and \( m \) is/are possible?
- \( n = 1, m = 1 \)
- \( n = 2, m = 2 \)
- \( n = 3, m = 1 \)
- \( n = 4, m = 4 \)
The Correct Option is B, C
Solution and Explanation
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