Which of the following should be done in order to prepare $0.40 \ M \ NaCl$ starting with $100 \ mL$ of $0.30 \ M \ NaCl$ (mol.wt. of $NaCl = 58.5$)?

$200 \ mL$ of a mixture of $50\% \ H_2$,$40\% \ CH_4$ and $10\% \ CO_2$ is exploded with excess of oxygen in an eudiometry tube. The resultant mixture is cooled to room temperature and is passed through $aq. KOH$. Find volume contraction after passing through $KOH$ ................. $mL$

Chlorophyll extracted from the crushed green leaves was dissolved in water to make $2 \, L$ solution of $Mg$ of concentration $48 \, ppm$. The number of atoms of $Mg$ in this solution is $x \times 10^{20}$ atoms. The value of $x$ is (Nearest Integer) (Given : Atomic mass of $Mg$ is $24 \, g \, mol^{-1}$,$N_{A} = 6.02 \times 10^{23} \, mol^{-1}$)

Substance $A_2B_{(g)}$ can undergo decomposition to form two sets of products. If the molar ratio of $A_{2(g)}$ to $A_{(g)}$ is $5 : 3$ in a set of product gases,then the energy involved in the decomposition of $1 \, \text{mole}$ of $A_2B_{(g)}$ is:
$A_2B_{(g)} \to A_{2(g)} + B_{(g)}; \Delta H^o = 40 \, \text{kJ/mol}$
$A_2B_{(g)} \to A_{(g)} + AB_{(g)}; \Delta H^o = 50 \, \text{kJ/mol}$

Iron sulphide is heated in air to form $A$,an oxide of sulphur. $A$ is dissolved in water to give an acid. The basicity of this acid is:

$1 \ g$ equivalent of a substance is present in: