Here's why:

* Chemical Structure: Atropine hydrogen sulfate is a salt formed by combining atropine (an alkaloid) with sulfuric acid. Salts are generally more soluble in water than their parent compounds.

* Polarity: The sulfate ion (SO4²⁻) is highly polar, making the entire molecule more soluble in water, which is also a polar solvent.

Important Note: While atropine hydrogen sulfate is water soluble, it's crucial to handle it with caution as it's a potent drug with serious side effects. Always follow proper handling and dosage instructions from a qualified medical professional.