$25 \ mL$ of the given $HCl$ solution requires $30 \ mL$ of $0.1 \ M$ sodium carbonate solution. What is the volume of this $HCl$ solution required to titrate $30 \ mL$ of $0.2 \ M$ aqueous $NaOH$ solution? .............. $mL$

During the estimation of oxalic acid $V/S$ $KMnO_4$,the self-indicator is:

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 $K_{2}Cr_{2}O_{7} = 294 \, g \, mol^{-1}$]

Solution $X$ contains $Na_2CO_3$ and $NaHCO_3$. $20 \ mL$ of $X$ when titrated using methyl orange indicator consumed $60 \ mL$ of $0.1 \ M \ HCl$ solution. In another experiment,$20 \ mL$ of $X$ solution when titrated using phenolphthalein consumed $20 \ mL$ of $0.1 \ M \ HCl$ solution. The concentrations (in $mol \ L^{-1}$) of $Na_2CO_3$ and $NaHCO_3$ in $X$ are respectively:

The strength of an aqueous solution of $I_2$ can be determined by titrating the solution with a standard solution of:

For standardizing $NaOH$ solution,which of the following is used as a primary standard?