The hardness of a water sample (in terms of equivalents of $CaCO_3$) containing $10^{-3} \ M \ CaSO_4$ is ................... $ppm$ (Molecular mass of $CaSO_4 = 136 \ g \ mol^{-1}$)

$A$ flask is weighed when filled with methane $(CH_4)$. The methane is then removed,and the flask is weighed again. When the flask is filled with oxygen $(O_2)$ at the same temperature and pressure,the mass of oxygen will be:

Find the mass of sodium carbonate in grams required to prepare $100 \text{ ml}$ of a $0.1 \text{ M}$ aqueous solution. (Molar mass of $Na_2CO_3 = 106 \text{ g/mol}$) (in $\text{ g}$)

The molar solution of sulphuric acid is equal to:

The active mass of benzene $(C_6H_6 = 78)$ with a density of $1.56 \, g/mL$ is .......

Excess of carbon dioxide is passed through $50 \ mL$ of $0.5 \ M$ calcium hydroxide solution. After the completion of the reaction,the solution was evaporated to dryness. The solid calcium carbonate was completely neutralized with $0.1 \ N$ hydrochloric acid. The volume of hydrochloric acid required is (Atomic mass of calcium $= 40$ ) (in $cm^{3}$)