Chapter 2 - Polar Covalent Bonds; Acids and Bases - Exercises - Page 59h: 63

In scenario a, there is no dipole moment. In scenario b, there is dipole moment. In scenario c, there is no dipole moment.

In scenario a, carbonate ion is planar and symmetrical and it has no dipole moment. In scenario b, diethyl ether has two singular pairs which causes a dipole moment. In scenario c, it is a symmetrical and planar and symmetrical and it has no dipole moment.