The linear structure is assumed by;

The question asks which species are assumed to have a linear structure.

Option (1) SnCl₂ is not linear. In the gas phase the tin atom uses an sp² hybridisation, giving a trigonal‑pyramidal (or V‑shaped) geometry with a lone pair on tin.

Option (2) NCO^‑ (the cyanate ion) contains a carbon atom bonded to nitrogen and oxygen. The central carbon is sp‑hybridised, forming a triple‑bond‑like arrangement N≡C–O⁻. The two regions of electron density lie opposite each other, resulting in a linear N–C–O arrangement.

Option (3) CS₂ (carbon disulphide) also has a central carbon atom that is sp‑hybridised. It forms two double bonds C=S that are arranged 180° apart, giving a linear S–C–S geometry.

Since both NCO^‑ (2) and CS₂ (3) are linear, the correct choice is “Both (2) and (3)”.

Therefore, the linear structure is assumed by the species listed in options (2) and (3).