**Core Concept**
The synthesis of urea in the liver involves the urea cycle, a series of enzyme-catalyzed reactions that convert ammonia (NH3) into urea. This process requires energy, which is primarily generated by the hydrolysis of ATP.

**Why the Correct Answer is Right**
The correct answer is based on the urea cycle's stoichiometry. The urea cycle involves the conversion of ammonia (NH3) into urea, which requires the following steps:
- The hydrolysis of ATP to ADP and phosphate (Pi) to provide energy for the reaction.
- The combination of ammonia (NH3) and carbon dioxide (CO2) to form carbamoyl phosphate, which is then converted to citrulline.
- Citrulline is then converted to argininosuccinate, which is finally converted to arginine and then to urea.
The hydrolysis of one molecule of ATP provides the energy required for the synthesis of one mole of urea.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because it does not accurately reflect the number of ATP molecules required for the synthesis of one mole of urea.
* **Option B:** This option is incorrect because it suggests that a different number of ATP molecules is required for the synthesis of one mole of urea.
* **Option D:** This option is incorrect because it suggests that a different number of ATP molecules is required for the synthesis of one mole of urea.

**Clinical Pearl / High-Yield Fact**
The urea cycle is an important mechanism for detoxifying ammonia in the liver, but it can be impaired in certain conditions, such as liver disease or ornithine transcarbamylase deficiency.

**Correct Answer:** 3. 3 ATP molecules are required for the synthesis of 1 mole of urea.