Which of the following molecules has a linear shape?

Step 1: Analyze the question We need the molecule whose atoms lie in a straight line (bond angle 180°). We use VSEPR theory (Valence Shell Electron Pair Repulsion): electron pairs around the central atom repel each other and spread as far apart as possible.

Step 2: Check each option

• A. CH₄: Carbon has 4 bond pairs and no lone pairs. The shape is tetrahedral (109.5°).
• B. CO₂: Carbon has 2 double bonds (O=C=O) and no lone pairs. With only 2 regions of electron density, they sit opposite each other, so the shape is linear (180°).
• C. H₂S: Sulfur has 2 bond pairs and 2 lone pairs. The lone pairs push the bonds together, giving a bent (V-shaped) molecule (about 92°–105°).
• D. NH₃: Nitrogen has 3 bond pairs and 1 lone pair. The shape is trigonal pyramidal (about 107°).

Step 3: Conclusion Only CO₂ has no lone pairs on the central atom and just two regions of electron density, so it is linear.

Answer: B. CO₂

Exam tip: Remember the linear molecules: CO₂, BeCl₂, and C₂H₂ (ethyne). If the central atom has 2 electron regions and no lone pairs, the molecule is linear. If lone pairs are present, as in H₂O and H₂S, the shape is bent.