With $z$ along C=O and the molecule in the $xz$ plane, <formaldehyde> has $E$, $C_2(z)$, $\sigma_{xz}$ and $\sigma_{yz}$. It belongs to the <C2v point group>, $\boxed{C_{2v}}$. Keeping this axis convention is essential when assigning the labels $B_1$ and $B_2$.

Solution

Past exam of the chemistry A course of the University of Cambridge / 2025 / Paper 1 / A4 / b / i / Solution

 Solution (source code)