You want the molecule that is symmetrical in the 3 dimensional shape. Do you know the shapes of these molecules?
The molecular geometry?
The last two are bent?, I believe. (d,e) Hydrogen can only make a single bond, right?
Um. The first has zero lone pairs and four bonds, so it's tetrahedral, maybe. (a)
I think the third is trigonal planar. (c)
And the second is.... uh, like one lone pair and three bonds. So, trigonal pyramidal, then.
OK. You know the shapes rather well. So a is tetrahedral; however, with 3 H and 1 Cl, it cannot be symmetrical so it will have a net dipole moment. NH3 is trigonal pyramidal (tetrahedral electronic geometry) so it will have 3 Hs and a lone pair so it will not be symmetrical and will have a net dipole moment. Following that line of reasoning, which do you think is symmetrical, which means no net dipole moment.
Since the first two are bent then they will have a dipole moment, also.
BCl3 has equally spaced bonds between its three, so that one would be symmetrical, meaning no dipole moment.