What is the value of percent atom economy when an organic compound of formula weight $$75 \mathrm{~u}$$ is obtained from reactants having sum formula weight $$225 \mathrm{~u}$$ ?

Which from following substances consists of total 1 mole atoms in it? (Molar mass of $$\mathrm{NH}_3=17, \mathrm{H}_2 \mathrm{O}=18, \mathrm{~N}_2=28, \mathrm{CO}_2=44$$ )

How many moles of nitrogen atoms are present in $$8 \mathrm{~g}$$ of ammonium nitrate?

(Molar mass of ammonium nitrate $$=80$$ )

Calculate the $$\mathrm{pH}$$ of a buffer solution containing $$0.01 ~\mathrm{M}$$ salt and $$0.004 \mathrm{~M}$$ weak acid.

$$\left(\mathrm{pK}_{\mathrm{a}}=4.762\right)$$