Consider the following statements.
I. The pH of a mixture containing 400ml of 0.1M ${\mathrm{H}}_2{\mathrm{SO}}_4$ and 400ml of 0.1M NaOH will be approximately 1.3.
II. The Ionic product of water is temperature- dependent.
III. Le-chatelier’s principle is applicable to the common-ion effect.
IV. A mixture of ${\mathrm{HClO}}_4+{\mathrm{NaClO}}_4$ acts as an acidic buffer.
The correct statements are 

I :  ${\mathrm{N}}_{\mathrm{mix}}=\frac{{\mathrm{V}}_{\mathrm{a}}{\mathrm{N}}_{\mathrm{a}}-{\mathrm{V}}_{\mathrm{b}}{\mathrm{N}}_{\mathrm{b}}}{{\mathrm{V}}_{\mathrm{a}}+{\mathrm{V}}_{\mathrm{b}}}=\frac{80-40}{800}=\frac{40}{800}=\frac{1}{20}=5\times {10}^{-2}$

                 For S.A. [H⁺] = N =$5\times {10}^{-2}$  ; P^H = 2- 1og5=2-0.7=1.3
      II: As temperature increases K_W will increase
${\mathrm{K}}_{\mathrm{W}}$  at $5^0\mathrm{C}=0.186\times {10}^{-14}{\mathrm{mole}}^2/{\mathrm{Lit}}^2$

$K_W$   at ${25}^0\mathrm{C}=1.008\times {10}^{-14}{\mathrm{mole}}^2/{\mathrm{Lit}}^2$

III. In the presence of common ion the degree of dissociation of weak electrolyte decreases.
        Ex: In presence of NH₄Cl, the dissociation of NH₄OH decreases due to common ion effect.
IV. Acidic buffer is a mixture of W.A+Slat with strong base. Here HClO4 is a strong acid and NaClO4 is a salt of Strong Acid and strong Base.  Hence S(IV) is not correct.

$C{H}_{3}COOH\rightleftharpoons C{H}_{3}CO{O}^{-}+H^{+}$

$C{H}_{3}COONa\to C{H}_{3}CO{O}^{-}+N{a}^{+}$

IV. Acidic buffer is a mixture of W.A+Salt with a strong base. Here HClO₄ is a strong acid and NaClO₄ is a salt of strong acid and a strong base.  Hence, Statement (IV) is not correct.