When a standard solution of $NaOH$ is left in the air for a few hours,

Which of the following statements regarding $pH$ and $[H^+]$ is incorrect?

At $27^{\circ}C$,$100 \ mL$ of $0.4 \ M$ $HCl$ is mixed with $100 \ mL$ of $0.5 \ M$ $NaOH$ solution. To the resultant solution,$800 \ mL$ of distilled water is added. What is the $pH$ of the final solution?

The correct order of increasing $[H_3O^{+}]$ in the following aqueous solutions is:

What is the percent dissociation of $NH_4OH$ if the molar conductance at zero concentration for $NH_4Cl, NaCl$,and $NaOH$ are $130, 109$,and $213 \ S \ cm^2 \ mol^{-1}$ respectively,and the molar conductivity of $0.01 \ M \ NH_4OH$ is $9.0 \ S \ cm^2 \ mol^{-1}$?

At $25\, ^oC$,the dissociation constant of $CH_3COOH$ and $NH_4OH$ in aqueous solution are almost the same. The $pH$ of a $0.01\, N$ $CH_3COOH$ solution is $4.0$ at $25\, ^oC$. The $pH$ of a $0.01\, N$ $NH_4OH$ solution at the same temperature would be: