Which of the substances is non-polar?

Step 1: Analyze the question We need to find the substance whose molecules are non-polar, meaning there is no uneven distribution of charge across the molecule.

Step 2: Key concept A molecule is polar if:

• its bonds are polar (the atoms differ in electronegativity), and
• the molecule's shape does not cancel out those bond dipoles.

A molecule is non-polar if it is made of identical atoms (no electronegativity difference) or has a perfectly symmetrical shape.

Step 3: Check each option

• A. Bromine (Br₂): Both atoms are identical, so the electronegativity difference is zero. The shared electrons are pulled equally and there is no dipole. Non-polar.
• B. Ammonia (NH₃): N is more electronegative than H, and the molecule is pyramidal with a lone pair on N. The dipoles do not cancel, so it is polar.
• C. Water (H₂O): O is more electronegative than H, and the molecule is bent (V-shaped). The dipoles do not cancel, so it is polar.
• D. Hydrogen bromide (HBr): Br is more electronegative than H, so the bond is polar and the molecule is a dipole. It is polar.

Step 4: Answer Bromine is the only substance made of two identical atoms joined by a purely covalent (non-polar) bond, so it is A.

Exam tip: Diatomic molecules of the same element (H₂, O₂, N₂, Cl₂, Br₂, I₂) are always non-polar. If you see one among the options, it is very likely the answer to a "non-polar" question. For molecules with different atoms, check the shape: symmetrical ones such as CO₂, CH₄ and BF₃ are non-polar, while bent or pyramidal ones such as H₂O and NH₃ are polar.