Calculate mass in kg of 2.5 mole ammonia.

Find the number of moles of sodium atoms in $6.9 \times 10^{-2} \mathrm{~kg}\left(\right.$ Atomic mass $\left.=23 \mathrm{~g} \mathrm{~mol}^{-1}\right)$

What is the percentage by mass of oxygen in NaOH ? (Atomic mass of $\mathrm{Na}=23 \mathrm{u}, \mathrm{O}=16 \mathrm{u}, \mathrm{H}=1 \mathrm{u}$ )

What is value of percent atom economy when reactants having sum of formula weight 78 u results in the formation of a product with formula weight 65 u ?