Which of the following absorbs oxygen rapidly?

Formic acid $(HCOOH)$ is a weak acid and hydrochloric acid $(HCl)$ is a strong acid. It follows that the:

When $CO_2$ dissolves in water,the following equilibrium is established:
$CO_2 + 2H_2O \rightleftharpoons H_3O^{+} + HCO_3^-$
For which the equilibrium constant is $3.8 \times 10^{-7}$ and $pH = 6.0$. The ratio of $[HCO_3^-]$ to $[CO_2]$ would be:

Consider the following statements:
$(a)$ The $pH$ of a mixture containing $400 \, mL$ of $0.1 \, M \, H_2SO_4$ and $400 \, mL$ of $0.1 \, M \, NaOH$ will be approximately $1.3$.
$(b)$ Ionic product of water is temperature dependent.
$(c)$ $A$ monobasic acid with $K_a = 10^{-5}$ has a $pH = 5$. The degree of dissociation of this acid is $50 \%$.
$(d)$ The Le Chatelier's principle is not applicable to common-ion effect.
The correct statements are:

What is the $[OH^{-}]$ in the final solution prepared by mixing $20.0 \ mL$ of $0.050 \ M \ HCl$ with $30.0 \ mL$ of $0.10 \ M \ Ba(OH)_2$? $...... \ M$

The solubility product of a sparingly soluble salt $A_{2}X_{3}$ is $1.1 \times 10^{-23}$. If specific conductance of the solution is $3 \times 10^{-5} \ S \ m^{-1}$,the limiting molar conductivity of the solution is $x \times 10^{-3} \ S \ m^{2} \ mol^{-1}$. The value of $x$ is ...