Identify a pair of molecules having zero dipole moment.

The dipole moment of a molecule depends on its geometry and the polarity of its bonds.

$\text{BF}_3$ has a symmetrical trigonal planar geometry, so its dipole moment is zero. However, $\text{HBr}$ is a polar diatomic molecule with a non-zero dipole moment.

$\text{CH}_4$ has a symmetrical tetrahedral geometry, so its dipole moment is zero. $\text{NF}_3$ has a trigonal pyramidal geometry with a lone pair on nitrogen, resulting in a non-zero dipole moment.

$\text{NH}_3$ and $\text{H}_2\text{O}$ have trigonal pyramidal and bent geometries respectively, both possessing lone pairs that lead to non-zero dipole moments.

$\text{CCl}_4$ has a symmetrical tetrahedral geometry, causing the individual $\text{C-Cl}$ bond dipoles to cancel out, resulting in a zero dipole moment.

$\text{CO}_2$ has a linear geometry, where the two $\text{C=O}$ bond dipoles are equal and opposite, cancelling each other out to give a zero dipole moment.

Thus, both $\text{CCl}_4$ and $\text{CO}_2$ have zero dipole moments.

Answer: $\text{CCl}_4$ and $\text{CO}_2$