Which of the following compounds have a nonzero dipole moment?

Question

Which of the following compounds have a nonzero dipole moment?
a) SiBrH3 b) NH4+ c) GaH3 d) H2

must enter all tru statements

Answer 1

two things are required for a nonzero dipole moment

-the molecule must have polar bonds
-the molecule must NOT be symmetrical

b c and d are symmetrical. a has polar bonds and is not symmetrical, so a is the answer.

edit: there are no nonbonding valence electrons in GaH3:

http://www.webelements.com/webelements/elements/text/Ga/econ.html

Answer 2

Nonzero Dipole Moment

Answer 3

a) has a dipole moment
c) do a Lewis structure for this one. You'll see non-bonding electrons which force the 3 H toward one another, making it have a dipole moment.