(a) CCl4 (carbon tetrachloride): Nonpolar. It is composed of nonpolar C-Cl bonds and has a symmetrical shape.
(b) NH3 (ammonia): Polar. It has an unequal distribution of charges due to the lone pair of electrons on the nitrogen atom.
(c) SF4 (sulfur tetrafluoride): Polar. The sulfur atom has a higher electronegativity than the fluorine atoms, creating polar S-F bonds.
(d) XeF4 (xenon tetrafluoride): Nonpolar. The xenon and fluorine atoms have similar electronegativities, resulting in nonpolar bonds. The molecule also has a symmetrical tetrahedral shape.
(e) CH3Br (methyl bromide): Nonpolar. The polar C-Br bond is surrounded symmetrically by nonpolar C-H bonds. The effects cancel out, resulting in a nonpolar molecule.
(f) GaH3 (gallium trihydride): Nonpolar. The gallium and hydrogen atoms have similar electronegativities, creating nonpolar Ga-H bonds. The molecule also has a symmetrical trigonal planar shape.