The pair from the following pairs having both compounds with net non-zero dipole moment is

🧠 A pair has both non-zero dipole moments only if both molecules are asymmetric (no symmetry element that cancels bond dipoles).

🗺️ Analyse each pair:

(1) 1,4-Dichlorobenzene and 1,3-Dichlorobenzene:

• 1,4-: two Cl atoms directly opposite → bond dipoles cancel → μ = 0 ✗
• 1,3-: two Cl atoms at 60° angle → partial cancellation → μ ≠ 0 ✓
• Pair fails (one has μ = 0)

(2) cis-butene and trans-butene:

• cis-butene: slight dipole (polar) ✓
• trans-butene: symmetric → μ = 0 ✗
• Pair fails

(3) $\mathrm{CH_2Cl_2}$ and $\mathrm{CHCl_3}$:

• $\mathrm{CH_2Cl_2}$ (tetrahedral, two H and two Cl): asymmetric → μ ≠ 0 ✓
• $\mathrm{CHCl_3}$ (one H, three Cl): asymmetric → net dipole ≠ 0 ✓
• Both non-zero ✓

(4) Benzene and anisidine:

• Benzene: symmetric → μ = 0 ✗

$\boxed{\text{Answer: } \mathrm{CH_2Cl_2} \text{ and } \mathrm{CHCl_3}}$