$A$ mixture of $O_2$ and gas $Y$ (molecular weight $80$) in the mole ratio $a : b$ has a mean molecular weight of $40$. What would be the mean molecular weight if the gases are mixed in the ratio $b : a$ under identical conditions? (The gases are non-reacting)

If $10^{23}$ molecules are removed from $5.6 \ L$ of an ideal gas at $273 \ K$ and $2 \ atm$ pressure,how many moles of the gas will remain?

State whether the following statements are true or false:
$(i)$ The molarity of a $0.6 \ N$ aqueous solution of ${H_3PO_3}$ is $1.2 \ M$.
$(ii)$ $\text{Empirical formula} = n \times \text{Molecular formula}$.
$(iii)$ In ${Cl_2O}$,the weight of chlorine combining with $8 \ g$ of oxygen is $35.5 \ g$.

$K_2CS_3$ can be called potassium:

Which is the correct option for $0.1 \ M$,$500 \ mL$ of $AgCl$?

Air contains $23\% \, O_2$ and $77\% \, N_2$ by weight. What is the percentage of $O_2$ by volume?