In the titration of $Na_2CO_3$ with $HCl$ using phenolphthalein as an indicator,what will be the result?

$20 \, mL$ of calcium hydroxide was consumed when it was reacted with $10 \, mL$ of an unknown solution of $H_2SO_4$. Also,$20 \, mL$ of a standard solution of $0.5 \, M$ $HCl$ containing $2$ drops of phenolphthalein was titrated with calcium hydroxide. The mixture showed a pink color when the burette displayed the value of $35.5 \, mL$,whereas the burette showed $25.5 \, mL$ initially. The concentration of $H_2SO_4$ is $..........M$ (Nearest integer).

When $10 \ mL$ of an aqueous solution of $Fe^{2+}$ ions was titrated in the presence of dil $H_{2}SO_{4}$ using diphenylamine indicator,$15 \ mL$ of $0.02 \ M$ solution of $K_{2}Cr_{2}O_{7}$ was required to get the end point. The molarity of the solution containing $Fe^{2+}$ ions is $X \times 10^{-2} \ M$. The value of $x$ is $....$ (Nearest integer)

The amount of oxalic acid present in a solution can be determined by its titration with $KMnO_4$ solution in the presence of $H_2SO_4$. The titration gives an unsatisfactory result when carried out in the presence of $HCl$,because $HCl$:

$A$ $100 \ mL$ solution of $0.1 \ N \ HCl$ was titrated with $0.2 \ N \ NaOH$ solution. The titration was discontinued after adding $30 \ mL$ of $NaOH$ solution. The remaining titration was completed by adding $0.25 \ N \ KOH$ solution. The volume of $KOH$ required for completing the titration is $..... \ mL$

In a titration experiment,$10 \, mL$ of an $FeCl_{2}$ solution consumed $25 \, mL$ of a standard $K_{2}Cr_{2}O_{7}$ solution to reach the equivalence point. The standard $K_{2}Cr_{2}O_{7}$ solution is prepared by dissolving $1.225 \, g$ of $K_{2}Cr_{2}O_{7}$ in $250 \, mL$ water. The concentration of the $FeCl_{2}$ solution is closest to $..... \, N$
[Given : molecular weight of $K_{2}Cr_{2}O_{7} = 294 \, g \, mol^{-1}$]