Match each quantity to what it represents.

• Polarisation $\mathbf{P}$ → Dipole moment per unit volume
• Displacement field $\mathbf{D}$ → Lets Gauss’s law be applied to free charge alone
• Susceptibility $\chi_e$ → How strongly the medium polarises per unit field
• Relative permittivity $\varepsilon_r$ → The factor by which the field is weakened

$\mathbf{P}$ measures the aligned dipoles, $\mathbf{D}$ hides them from Gauss’s law, $\chi_e$ sets how readily they align, and $\varepsilon_r = 1 + \chi_e$ is the resulting field reduction.