Which of the following triatomic molecules does not exist?

What is the total number of planes in $CH_4$ that contain the maximum number of atoms?

In which of the following pairs is the geometry around the central atom not the same?

Compare the $x$ and $y$ bond lengths in the following molecules:
Structure $1$: $HO-S(=O)-S(=O)-OH$ (where $x$ is the $S-S$ bond length)
Structure $2$: $HO-S(=O)_2-S(=O)-OH$ (where $y$ is the $S-S$ bond length)

Which of the following species is not a pseudo-halide?

In solid state,$PCl_5$ is a/an