Final answer:
The molecular shape of acetylene (C2H2) is linear, due to the presence of a C≃C triple bond, and only two groups of electrons around each carbon atom.
Step-by-step explanation:
The molecular shape of acetylene (C₂H₂) is linear. In the acetylene molecule, there are two C-H sigma bonds and a C≃C triple bond, which consists of one C-C sigma bond and two C—C pi bonds. This structure is represented by the overlapping of the four unhybridized p orbitals side-by-side, creating a linear geometry. Double or triple bonds count as a single electron group, resulting in a linear shape because there are only two groups of electrons around each carbon atom in acetylene. Therefore, the correct answer is (a) Linear.