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

We need to find the pair where both compounds have a net non-zero dipole moment.

We start by noting that

A molecule has a non-zero dipole moment when the bond dipoles do not cancel due to molecular asymmetry. Symmetric molecules (like linear CO$$_2$$, benzene, para-dichlorobenzene, trans-butene) have zero dipole moments.

Next,

Option 1: 1,4-Dichlorobenzene and 1,3-Dichlorobenzene

1,4-Dichlorobenzene (para): The two C-Cl bond dipoles are equal and opposite, cancelling exactly. Dipole moment = 0.

1,3-Dichlorobenzene (meta): The bond dipoles do not cancel. Dipole moment is non-zero.

Not both non-zero.

Option 2: cis-butene and trans-butene

cis-2-butene: The two CH$$_3$$ groups are on the same side, creating asymmetry. Has a small but non-zero dipole moment.

trans-2-butene: The CH$$_3$$ groups are on opposite sides, and the molecule has a centre of symmetry. Dipole moment = 0.

Not both non-zero.

Option 3: CH$$_2$$Cl$$_2$$ and CHCl$$_3$$

CH$$_2$$Cl$$_2$$ (dichloromethane): Tetrahedral with 2 H and 2 Cl -- asymmetric arrangement. Has a dipole moment of 1.60 D. Non-zero.

CHCl$$_3$$ (chloroform): Tetrahedral with 1 H and 3 Cl -- asymmetric. Has a dipole moment of 1.04 D. Non-zero.

Both have non-zero dipole moments.

Option 4: Benzene and anisidine

Benzene is perfectly symmetric with zero dipole moment.

Not both non-zero.

The correct answer is Option 3: CH$$_2$$Cl$$_2$$, CHCl$$_3$$.