Which formula represents a polar molecule?
(1) h2 (3) co2
(2) h2o (4) ccl4

Molecules are said to be polar when there is a net dipole moment. 3D structures of molecules play an important role in this effect. Symmetrical molecules cancel out net dipile to 0.

H2, CO2 and CCl4 are all symmetrical, thus are non-polar.

H2O is structurally bent. It is polar.

Copper, silver, aluminum, cobalt, chromium, mercury