Here's why:

* Acetone's Structure: Acetone (CH₃COCH₃) has a central carbonyl group (C=O). The carbon in this group is double-bonded to oxygen and single-bonded to two methyl groups (CH₃).

* Oxygen's Valence Electrons: Oxygen has six valence electrons.

* Oxygen's Bonding: In the carbonyl group, oxygen forms a double bond with carbon, using two of its valence electrons.

* Lone Pairs: The remaining four valence electrons on the oxygen atom form two lone pairs.

Therefore, acetone has two lone pairs of electrons on its oxygen atom.