Experimentally determined analytical data for PhSeCl₃ are C, 27.5; H, 1.8; Cl, 39.9%. An X-ray diffraction study of PhSeCl₃ shows that it forms polymeric chains in the solid state, with each Se centre in a square-based pyramidal environment with the Ph group in the axial position. 

(a) To what extent are elemental analytical data useful in characterizing a new compound? 

(b) Draw part of the polymeric chain from the solid state structure, paying attention to the overall stoichiometry of the compound. 

(c) Around one Se centre in the solid state structure of PhSeCl₃, the observed Se–Cl bond distances are 220, 223, 263 and 273pm. Comment on these values in the light of your answer to part (b).