Which of the following attain the linear structure: i. BeCl2 ii. NCO+ iii. NO2 iv. CS2​

A.(nh4)(2co3)is the correct answer 

Ch4 and ph3 are both covalent since they are composed both of non-metals.    ch4 is non- polar because of  london forces and has a geometry of tetrahedral  ph3 , on the other hand, is umbrella shaped polar and has dipole-dipole intermolecular force (imf) . since ph3 is polar, it has a stronger imf