The GATE Grind

GATE 2024 CY – Question 57

Physical Chemistry · Group Theory: Symmetry elements and symmetry operations. Basic postulates of groups and group multiplication tables. Classes, reducible and irreducible representations of symmetry elements. Classification and labelling of molecular point groups. Symmetry based selection rules and their application to electronic and vibrational spectroscopy. Internal coordinates and symmetry labelling of vibrational modes; symmetry adapted linear combination of atomic orbitals (LCAO-MO); construction of hybrid orbitals using molecular point group symmetry. · 2 marks · Multiple select

Among the following, the correct statement(s) is (are):

  1. $C_2$ symmetry element is present in $\mathrm{H_2O}$ and $\mathrm{H_2O_2}$ but NOT in $\mathrm{PCl_5}$.
  2. both $C_2$ and $C_3$ symmetry elements are present in $\mathrm{CCl_4}$ and $\mathrm{SF_6}$.
  3. one $\sigma_h$ and three $\sigma_d$ symmetry elements are present in benzene.
  4. $\sigma_v$ symmetry element is present in $\mathrm{NH_3}$ but NOT in $\mathrm{BF_3}$.

Practise this question in The GATE Grind →

Show answer and explanation

Correct answer: (B) both $C_2$ and $C_3$ symmetry elements are present in $\mathrm{CCl_4}$ and $\mathrm{SF_6}$.; (C) one $\sigma_h$ and three $\sigma_d$ symmetry elements are present in benzene.

Explanation

Check the symmetry statements.

Answer **B and C**.