(d)
Freundlich adsorption isotherm gives relationship between pressure and amount of substrate adsorbed.
$x/m = kp^{\frac{1}{n}}$ (where, $x/m = amount\ adsorbed\ ,p = pressure$)
or $x = m.kp^{\frac{1}{n}}$
or $x/m = kp^{- n}$
$\therefore$ All equations represent Freundlich adsorption isotherm.