Which of the following can be used to prevent the decomposition of $$H_2O_2$$?

Hydrogen peroxide (H₂O₂) tends to decompose into water and oxygen over time:

$$2H_2O_2 \rightarrow 2H_2O + O_2$$

To prevent this decomposition, a stabilizer is added that can inhibit the catalytic decomposition.

Analysis of options:

Option A: Urea

Urea is a well-known stabilizer for H₂O₂. It forms a stable adduct (urea hydrogen peroxide, UHP) with H₂O₂ and acts as a negative catalyst, slowing down the decomposition. It is commonly used in pharmaceutical and industrial applications to stabilize H₂O₂ solutions.

Option B: Formaldehyde

Formaldehyde is a reducing agent and can react with H₂O₂ rather than stabilize it.

Option C: Formic acid

Formic acid can react with H₂O₂ to form performic acid and is not used as a stabilizer.

Option D: Ethanol

Ethanol is an organic solvent that does not serve as an effective stabilizer for H₂O₂.

Therefore, the correct answer is Option A (Urea).