One litre of hard water contains $12.00 \ mg$ of $Mg^{2+}$. The milli-equivalents of washing soda $(Na_2CO_3)$ required to remove its hardness is:

$x$ grams of calcium carbonate was completely burnt in air. The weight of the solid residue formed is $28 \,g$. What is the value of $x$ (in grams)?

The yield of each step as actually carried out in the laboratory is given in the reaction scheme below. Calculate the overall percentage yield of the reaction.
$Me_3C-CO-CH_3$ $\xrightarrow{58\% (A)} Me_3C-CO-CH_2Br$ $\xrightarrow{54\% (B)} Me_3C-CH(OH)-CH_2Br$ $\xrightarrow{68\% (C)} Me_3C-CH(O)CH_2$

$2 \ g$ of aluminium is treated separately with excess of dilute $H_{2}SO_{4}$ and excess of $NaOH$. The ratio of the volumes of hydrogen evolved is

$100 \ mL$ of $0.1 \ N$ hypo solution is decolourised by the iodine liberated from the addition of $x \ g$ of crystalline copper sulphate to an excess of $KI$. The value of $x$ is ............. $g$ (molecular weight of $CuSO_4 \cdot 5H_2O$ is $250$).

Excess of $NaOH\, (aq)$ was added to $100\, mL$ of $FeCl_3\, (aq)$ resulting in $2.14\, g$ of $Fe(OH)_3$. The molarity of $FeCl_3\, (aq)$ is (Given molar mass of $Fe=56\, g\, mol^{-1}$ and molar mass of $Cl=35.5\, g\, mol^{-1}$) (in $, M$)