Past exam of the chemistry A course of the University of Cambridge / 2024 / Paper 1 / A4 / a / ii / Solution

One choice is the C2v molecular point group, $\{E,C_2(z),{\sigma }_{xz},{\sigma }_{yz}\}$. The additional operation is a second reflection, sinceA bent water molecule has this symmetry. Choose the $z$ axis along its bond-angle bisector and put the molecule in the $xz$ plane: reflection in $yz$ exchanges its two hydrogen atoms, while reflection in $xz$ fixes their positions.