What do you call the compounds having the same molecular formula but different structural arrangement of atoms?

16 Write the structural formulae of propyne. 17 write the structural formula of butane. 19 write the names of any two isomers represented by the molecular formula C₅H₁₂. 20 Write down (i) structural formula, and (ii) electron-dot formula, of any one isomer of hexane (C₆H₁₄), other than n-hexane.