What are the different elements present in the mineral barite?

Arrange the following in the order of increasing mass (atomic mass: $O = 16, Cu = 63, N = 14$)
$I.$ one atom of oxygen
$II.$ one atom of nitrogen
$III.$ $1 \times 10^{-10}$ mole of oxygen
$IV.$ $1 \times 10^{-10}$ mole of copper

Substance $A_2B_{(g)}$ can undergo decomposition to form two sets of products. If the molar ratio of $A_{2(g)}$ to $A_{(g)}$ is $5 : 3$ in a set of product gases,then the energy involved in the decomposition of $1 \, \text{mole}$ of $A_2B_{(g)}$ is:
$A_2B_{(g)} \to A_{2(g)} + B_{(g)}; \Delta H^o = 40 \, \text{kJ/mol}$
$A_2B_{(g)} \to A_{(g)} + AB_{(g)}; \Delta H^o = 50 \, \text{kJ/mol}$

If lattice enthalpy and hydration enthalpy of $KCl$ are $699 \ kJ \ mol^{-1}$ and $-681.8 \ kJ \ mol^{-1}$ respectively,what is the enthalpy of solution of $KCl$?

Calculate the number of moles of $NaOH$ required to completely neutralize $100 \ g$ of $118\%$ oleum.

Nitrogen atom has an atomic number of $7$ and oxygen has an atomic number of $8$. The total number of electrons in a nitrate ion $(NO_3^-)$ will be: