Answer:-

a. Atom economy is a measure of the number of atoms from the starting materials that are present in the useful products at the end of the chemical process.

b. Good atom economy means most of the atoms of the reactants are incorporated in the desired products, and only small amounts of unwanted by-products are formed, hence leading to fewer problems with waste disposal.

Illustration: The concept of atom economy gives the measure of the unwanted product produced in a particular reaction.

% atom economy = Formula weight of the desired product / Sum of formula weight of all the reactants used in the reaction × 100

For example: Conversion of Butan-1-ol to 1-bromobutane

\[\ce{CH3CH2CH2CH2OH + NaBr + H2SO4 -> CH3CH2CH2CH2Br + NaHSO4 + H2O}\]

% atom economy = (mass of (4C + 9H + 1Br) atoms) / (mass of (4C + 12H + 5O + 1Br + 1Na + 1S) atoms) × 100

= (137 u) / (275 u) × 100 = 49.81%