Which of the following has a $pH$ of $12$?

The $pH$ of $\frac{N}{100}$ $HCl$ would be approximately

Calculate the $pH$ of $1.0 \times 10^{-8} \ M \ NaOH$ solution.

Aqueous solution of $HCl$ has the $pH = 4$. Its molarity would be (in $, M$)

Calculate $pH$ and $pOH$ of $0.03 \ M$ $NaOH$ solution.

Five solutions of $KOH$ are prepared as follows: $1st \to 0.1 \ mol$ in $1 \ L$,$2nd \to 0.2 \ mol$ in $2 \ L$,$3rd \to 0.3 \ mol$ in $3 \ L$,$4th \to 0.4 \ mol$ in $4 \ L$,$5th \to 0.5 \ mol$ in $5 \ L$. What is the $pH$ of the resulting mixture?