The number of species from the following that have pyramidal geometry around the central atom is ____ {S_2O_3^{2-},\…

🧠 Pyramidal geometry requires a central S with 3 bonds + 1 lone pair (steric number 4, with 1 LP). Determine the structure of each sulfur-oxygen species.

| Species | S bonds | LP on S | Shape | |---|---|---|---| | $\ce{SO4^{2-}}$ | 4 bonds (to 4 O) | 0 | Tetrahedral | | $\ce{SO3^{2-}}$ | 3 bonds (to 3 O) | 1 | Pyramidal ✓ | | $\ce{S2O3^{2-}}$ | Central S: 4 bonds | 0 | Tetrahedral at S | | $\ce{S2O7^{2-}}$ | Each S: 4 bonds (3 O + 1 O bridge) | 0 | Tetrahedral at each S |

⚡ $\ce{SO3^{2-}}$ (sulfite) is the analogue of $\ce{SO3^{3-}}$... actually, $\ce{SO3^{2-}}$ has S with 6 valence e, 3 bonds to O, leaving 2e = 1 LP → pyramidal (isoelectronic with $\ce{PO3^{3-}}$ and $\ce{ClO3-}$).

$\boxed{\text{Answer: (d) 1}}$