Identify the element having outer electronic configuration $\mathrm{ns}^2 \mathrm{np}^5$.

What is the mass in kg of 5 mole of acetic acid $\left(\mathrm{mol}\right.$. mass $\left.=60 \mathrm{~g} \mathrm{~mol}^{-1}\right)$ ?

A solution of non volatile solute is obtained by dissolving 2 g in 50 g benzene. Calculate the vapour pressure of solution if vapour pressure of pure benzene is 640 mmHg at $25^{\circ} \mathrm{C}$. [mol. mass of benzene $=78 \mathrm{~g} \mathrm{~mol}^{-1}$, mol. mass of solute $\left.=64 \mathrm{~g} \mathrm{~mol}^{-1}\right]$

A gas absorbs certain amount of heat and expands by $200 \mathrm{~cm}^3$ against a constant external pressure of $2 \times 10^5 \mathrm{Nm}^{-2}$. What is work done by system?