Here's why:

* Polarity: Ammonium nitrate is a highly polar ionic compound, while acetone is a polar aprotic solvent. The difference in polarity makes it difficult for the ammonium nitrate to dissolve in acetone.

* Hydrogen Bonding: Ammonium nitrate can form strong hydrogen bonds with water, which is a highly polar solvent. Acetone, being less polar, cannot compete with water in forming these bonds.

In summary: While ammonium nitrate can dissolve in polar solvents like water, it is not soluble in acetone due to the difference in polarity and the ability to form strong hydrogen bonds.