Answer:
The dipole moment of a molecule depends on the magnitude and direction of the bond dipoles in the molecule. In water, the two O-H bonds are polar, meaning that they have a partial positive charge on the hydrogen atoms and a partial negative charge on the oxygen atom. This creates a net dipole moment for the molecule, with the negative end of the dipole moment located near the oxygen atom and the positive end located near the hydrogen atoms.
In contrast, CO2 has a linear geometry, with two polar C-O bonds oriented in opposite directions. The bond dipoles are equal in magnitude but opposite in direction, so they cancel each other out, resulting in a net dipole moment of zero.
Therefore, the dipole moment of CO2 is zero because the bond dipoles are symmetrically arranged and cancel out each other, while the dipole moment of water is nonzero because the bond dipoles are not symmetrically arranged and do not cancel out each other.