When $50 \ mL$ of $0.1 \ M$ $HCl$ and $50 \ mL$ of $0.2 \ M$ $NaOH$ solutions are mixed,the $pH$ of the resulting solution will be:

Given below are two statements :
Statement $I$ : Aqueous solution of ammonium carbonate is basic.
Statement $II$ : Acidic/basic nature of salt solution of a salt of weak acid and weak base depends on $K_a$ and $K_b$ value of acid and the base forming it.
In the light of the above statements,choose the most appropriate answer from the options given below :

The dissociation constant of a certain weak acid is $1.0 \times 10^{-4}$. What is the equilibrium constant for its reaction with a strong base?

Find the resulting $pH$ of the mixture of $200 \ mL$ of $HCl$ $(pH = 2)$ and $300 \ mL$ of $NaOH$ $(pH = 12.0)$.

The concentration of $[H^{+}]$ and concentration of $[OH^{-}]$ of a $0.1 \ M$ aqueous solution of $2\%$ ionised weak acid is [Ionic product of water $= 1 \times 10^{-14}$]

In a saturated solution of $Mg(OH)_2$,the degree of dissociation of $Mg(OH)_2$ is $\alpha$. Find the concentration $(C)$ of $Mg(OH)_2$ if the concentration of $[OH^{-}]$ is $2$.