Define: Atomicity.

Give any two examples for heterodiatomic molecules. 

What is Molar volume of a gas? 

Calculate the number of water molecules present in one drop of water which weighs $0.18\mathrm{g}$. 

${\mathrm{N}}_2+3{\mathrm{H}}_2\to 2{\mathrm{NH}}_3$

(The atomic mass of nitrogen is $14$, and that of hydrogen is $1$) 

$1$ mole of nitrogen (_____ $\mathrm{g}$) + $3$ moles of hydrogen (_____ $\mathrm{g}$)$\to$ $2$ moles of ammonia (_____ $\mathrm{g}$)

Calculate the number of moles in 

i) $27\mathrm{g}$ of $\mathrm{Al}$

ii) $1.51\times {10}^{23}$ molecules of ${\mathrm{NH}}_4\mathrm{Cl}$. 
 

Give the salient features of "Modern atomic theory".