Concept:
Punarnava is an Ayurvedic drug commonly used for its diuretic property.
Step 1: Diuretics increase urine output.
Step 2: Punarnava contains flavonoids and potassium salts.
Step 3: These constituents contribute to its diuretic activity.
Step 4: Hence, flavonoids and potassium salts are the correct constituents.
\[
\boxed{\text{Flavonoids and potassium salts}}
\]