Give the decreasing order of boiling points of the following:
(a).(I) Butanal
(II) Butane-1-ol
(III)Diethyl ether
(IV) Pentane
(b) (I) Propan`-2`-ol
(II) Propan`-2`-one
(III) `2-`Methyl propene

Explanation

To determine the decreasing order of boiling points for the given compounds in parts (a) and (b), we need to analyze the types of intermolecular forces present in each compound. The boiling point of a substance is influenced by the strength of these forces, which include hydrogen bonding, dipole-dipole interactions, and London dispersion forces.

### Part (a)

1. **Identify the compounds**:
- (I) Butanal
- (II) Butane-1-ol
- (III) Diethyl ether
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