The radius of the $Na^{+}$ ion is $95 \ pm$ and that of $Cl^{-}$ ion is $181 \ pm$. Predict the coordination number of $Na^{+}$ in $NaCl$.

Two flasks of equal volume are filled with $N_2$ gas and connected by a thin tube of negligible volume. When both flasks are immersed in boiling water,the pressure of the gas inside the system is $0.5 \, atm$. Calculate the pressure of the system when one flask is immersed in ice water and the other is kept in boiling water. (in $, atm$)

Which one of the following statements is not correct?

$1 \text{ mole}$ of gas $A$ and $1 \text{ mole}$ of gas $B$ at $27^{\circ} C$ were pumped into a $24.6 \ L$ volume pre-evacuated isolated flask. The catalyst coated inside the flask catalyses the following reaction $A_{(g)} + B_{(g)} \longrightarrow 2 D_{(g)}$. The kinetic energy of $D$ is $98.03 \ L \ atm$. Calculate the pressure realized at the end of the reaction. (in $atm$)

At the same temperature and pressure,the rate of diffusion of helium with respect to methane is ...... .

At $300 \ K$ and $760 \ torr$ pressure, the density of a mixture of $He$ and $O_2$ gases is $0.543 \ g \ L^{-1}$. The mass percent of oxygen is approximately $(R = 0.0821 \ L \ atm \ K^{-1} \ mol^{-1})$