Q.CO₂ and H₂O both are triatomic molecules but their dipole moment values are different. Why?

Step 1. Both CO₂ and H₂O are triatomic, AB₂-type molecules (one central atom bonded to two identical terminal atoms) — but their central atoms carry DIFFERENT numbers of lone pairs.

Step 2. CO₂'s carbon has 2 bond pairs (to the two oxygens, each a double bond) and ZERO lone pairs — 2 electron domains, sp hybridised, giving a LINEAR (180°) molecular shape.

Step 3. In this linear geometry, the two C=O bond dipoles point in exactly opposite directions and are equal in magnitude, so they cancel in vector sum: $\mu_{net} = 0$.

Step 4. H₂O's oxygen has 2 bond pairs (to the two hydrogens) PLUS TWO lone pairs — 4 electron domains, sp³ hybridised, giving a BENT (104.5°) molecular shape.

Step 5. In this bent geometry, the two O-H bond dipoles do NOT point in opposite directions (the angle between them is 104.5°, not 180°), so their vector sum is NON-zero: $\mu_{net} = 1.85$ D. …

Compare the central-atom lone-pair count of CO₂ (0) and H₂O (2) to establish their different VSEPR geometries (linear vs bent), then a …

• Assuming 'triatomic' by itself determines shape or polarity — the central atom's LONE-PAIR count (not just the total atom count) is what fixes the geometry and hence whether the bond dipoles cancel. …