If $20 \ mL$ of $0.4 \ N \ NaOH$ solution completely neutralises $40 \ mL$ of a dibasic acid,the molarity of the acid solution is $.......... \ M$.

If $8 \ g$ of $NaOH$ is dissolved in $1 \ L$ of solution,its molarity will be ....... $M$.

What is the volume (in $dm^3$) occupied by $75 \ g$ of ethane at $S$.$T$.$P$.?

If the percentage purity of an impure sample of a compound is given,then the weight of the substance required to prepare its $0.1 \, N$ solution will be:

$4.0 \ g$ of a mixture containing $Na_2CO_3$ and $NaHCO_3$ is heated to $673 \ K$. The loss in mass of the mixture is found to be $0.62 \ g$. The percentage of sodium carbonate in the mixture is:

$A$ sample of a metal oxide has the formula $M_{0.83}O_{1.00}$. The metal $M$ can exist in two oxidation states,$+2$ and $+3$. In the sample of $M_{0.83}O_{1.00}$,the percentage of metal ions existing in the $+2$ oxidation state is $.........\%$ (nearest integer).