Question

The correct order of heats of combustion of above compounds is:

• A. I > II > III
• B. II > I > III
• C. III > II > I
• D. III > I > II

Answer 1

The correct option is C III > II > I

The heat of combustion is the heat produced when one mole of a substance is completely burnt in oxygen under standard conditions.
Heat of combustion is directly proportional to the number of carbon atom for non-isomeric compound.
Here, compound (I) cyclopropane has 3 carbon cyclic chain.
Compound (II) cyclobutane has 4 carbon cyclic chain and compound (III) cyclopentane has 5 carbon cyclic chain.
Thus, the order of heat of combustion is,
III > II > I