If the reduction of a sample of $Cu_2O$ yields $1.27 \, g$ of $Cu$,then how many grams of oxygen must be present in it?

$10 \ mL$ of an aqueous solution containing $222 \ mg$ of calcium chloride $(mol. wt. = 111)$ is diluted to $100 \ mL$. The concentration of chloride ion in the resulting solution is $..... \ mol/L$.

Normality of $2 \, M$ sulphuric acid is

What is the value of percent atom economy when reactants having a sum of formula weight $78 \ u$ result in the formation of a product with a formula weight of $65 \ u$ (in $\%$)?

Equal masses of methane $(CH_4)$ and oxygen $(O_2)$ are mixed in an empty container at $25\,^oC$. The fraction of the total pressure exerted by oxygen is:

Sodium oxide reacts with water to produce sodium hydroxide. $20.0 \ g$ of sodium oxide is dissolved in $500 \ mL$ of water. Neglecting the change in volume,the concentration of the resulting $NaOH$ solution is $........ \times 10^{-1} \ M.$ (Nearest integer)
[Atomic mass $: Na=23.0, O=16.0, H=1.0]$