The degree of dissociation of $0.01 \ M$ solution of $NH_4OH$ is $4.2 \times 10^{-2}$. What is the percent dissociation of $NH_4OH$ (in $\%$)?

When dilute $H_2SO_4$ is added to an aqueous solution of potassium chromate,the yellow color of the solution changes to orange. This indicates that .....

Arrange the following resultant mixtures in increasing order of their pH values:
$A$. $10 \text{ mL } 0.2 \text{ M } Ca(OH)_2 + 25 \text{ mL } 0.1 \text{ M } HCl$
$B$. $10 \text{ mL } 0.01 \text{ M } H_2SO_4 + 10 \text{ mL } 0.01 \text{ M } Ca(OH)_2$
$C$. $10 \text{ mL } 0.1 \text{ M } H_2SO_4 + 10 \text{ mL } 0.1 \text{ M } KOH$
Choose the correct answer from the options given below:

Assign $A$,$B$,$C$,$D$ from the given type of reaction.
$BaSO_4(s) + Na_2CO_3(aq) \longrightarrow BaCO_3(s) + Na_2SO_4(aq)$

The initial rate of hydrolysis of methyl acetate $(1 \ M)$ by a weak acid $(HA, 1 \ M)$ is $1/100$th of that of a strong acid $(HX, 1 \ M)$ at $25^{\circ} C$. The $K_a$ of $HA$ is:

At $90 \, ^\circ C$,the concentration of $H^+$ and $OH^-$ ions in pure water is $10^{-6} \, M$. What is the value of $[H^+] + [OH^-]$ at this temperature?