The number of species from the following that have pyramidal geometry around the central atom is __________\( \mathrm{S_2O_3^{2-}},\ \mathrm{SO_4^{2-}},\ \mathrm{SO_3^{2-}},\ \mathrm{S_2O_7^{2-}} \)
\( 2 \)
\( 4 \)
\( 3 \)
\( 1 \)