The shapes of water, ammonia, carbon (iv) oxide and methane are respectively

Step 1: Analyze the question We need the molecular shapes of H₂O, NH₃, CO₂ and CH₄, in that order. The shape depends on the number of bonding pairs and lone pairs around the central atom (VSEPR theory).

Step 2: Concept (VSEPR) Electron pairs around the central atom repel each other and arrange themselves as far apart as possible. Lone pairs repel more strongly than bonding pairs, so they distort the shape.

Step 3: Work through each molecule

1. Water (H₂O): Oxygen has 2 bond pairs and 2 lone pairs. The shape is angular (bent), with a bond angle of about 104.5°.
2. Ammonia (NH₃): Nitrogen has 3 bond pairs and 1 lone pair. The shape is pyramidal (trigonal pyramidal), with a bond angle of about 107°.
3. Carbon (IV) oxide (CO₂): Carbon has 2 double bonds and no lone pairs. The shape is linear (O=C=O), with a bond angle of 180°.
4. Methane (CH₄): Carbon has 4 bond pairs and no lone pairs. The shape is tetrahedral, with a bond angle of 109.5°.

Step 4: Match to the options The order is angular, pyramidal, linear, tetrahedral.

Why the others are wrong:

• A: Water is not linear and CO₂ is not angular.
• C: Water is not pyramidal.
• D: Water is not tetrahedral in shape (its electron pair geometry is tetrahedral, but its molecular shape is angular).

Exam tip: Remember the pattern by the number of lone pairs on the central atom:

• CO₂: 0 lone pairs, 2 regions → linear
• CH₄: 0 lone pairs, 4 regions → tetrahedral
• NH₃: 1 lone pair → pyramidal
• H₂O: 2 lone pairs → angular

A handy memory line: "Water Bends, Ammonia Pyramids, CO₂ Lines up, Methane Tetra-hedrons."