What is the $pH$ of $0.005 \ M \ NaOH$ solution?

When $100 \ mL$ of $0.1 \ M$ $NaOH$ is added to $50 \ mL$ of $0.2 \ M$ $HCl$ at $25 \ ^oC$,the $pH$ of the resulting solution will be:

Find the number of equivalents of $HBr$ present in $100 \ mL$ of its solution whose $pH$ is $4$.

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?

The $pH$ of $100 \ mL$ of an aqueous solution of a strong acid is $1$. The volume of water to be added to change its $pH$ to $2$ is .......... $mL$.

The $pH$ of $0.01 \ N$ lime water is: