The $\mathrm{Fe}_2 \mathrm{O}_3-\mathrm{TiO}_2$ composite is used to adsorb the phosphate pollutant in waste water. The adsorption capacity of $\mathrm{Fe}_2 \mathrm{O}_3-\mathrm{TiO}_2$ composite for phosphate ions $(\theta=$ mass of phosphate ion in $\mathrm{mg} /$ mass of $\mathrm{Fe}_2 \mathrm{O}_3-\mathrm{TiO}_2$ composite in g ) from waste water as a function of equilibrium concentration of phosphate ion, i.e. $\left[\mathrm{PO}_4^{3-}\right]_{\text {eq. }}$. at two different pH of waste water at 300 K is shown in the figure below. The isotherms fit to the Freundlich adsorption isotherm. The correct option regarding the isotherm parameters $k$ and $n$, is

• Correct answer
  A

  Values of $k$ and $n$ at pH 5 are larger than those at pH 9 .
• B

  Values of $k$ and $n$ at pH 9 are larger than those at pH 5.
• C

  At the point P in the plots, the values of $k$ and $n$ for both the pH are same.
• D

  Value of $k$ is larger for pH 5 while $n$ is larger for pH 9 .

Hence, the correct answer is option: 'A'.