Find the mass of sodium carbonate in grams to form 100 ml 0.1 M solution in water?
( Molar mass of $\text{Na}_2\text{CO}_3$ = 106 g/mol)

What is number of hydrogen molecules needed to synthesize 3.4 g of ammonia by reaction with nitrogen?

If the velocity of the electron in Bohr's first orbit is $2.19 \times 10^6\ \text{Ms}^{-1}$, Calculate the de Broglie wavelength associated with it.
$[h = 6.626 \times 10^{-34}\ \text{J s}$ & Mass of electrons $= 9.10938 \times 10^{-31}$ kg $]$

Identify the group of periodic table that contains element Astatine.