**Core Concept**
Carbamide, also known as urea, is a compound used in dentistry for its bleaching properties. It is a popular alternative to hydrogen peroxide due to its stability and ease of use. However, its efficacy relies on its breakdown into hydrogen peroxide, the active bleaching agent.

**Why the Correct Answer is Right**
Carbamide solution degrades into hydrogen peroxide through a series of reactions involving the enzyme urease. The breakdown reaction is as follows: urea (carbamide) + 3H2O → 2(NH2)2CO + 2H+. The resulting carbamic acid then decomposes into ammonia (NH3) and carbon dioxide (CO2), releasing hydrogen peroxide (H2O2) in the process. The concentration of hydrogen peroxide produced is directly proportional to the concentration of carbamide used, typically resulting in a 3% solution.

**Why Each Wrong Option is Incorrect**
**Option A:** 0.3% sodium perborate is incorrect because carbamide does not degrade into sodium perborate. Sodium perborate is another type of bleaching agent, but it is not produced from the breakdown of carbamide.
**Option B:** 30% hydrogen peroxide is incorrect because the typical concentration of hydrogen peroxide produced from carbamide is 3%, not 30%. Higher concentrations of hydrogen peroxide can be obtained through other means, but not from carbamide degradation.
**Option D:** 30% sodium perborate is incorrect for the same reason as Option A: carbamide does not degrade into sodium perborate.

**Clinical Pearl / High-Yield Fact**
It's essential to note that the concentration of hydrogen peroxide produced from carbamide can vary depending on the specific product and brand used. Always check the manufacturer's instructions and follow proper usage guidelines to ensure safe and effective bleaching results.

**✓ Correct Answer: C. 3% hydrogen peroxide**