The reaction in photosynthesis where ATP is produced using sunlight occurs in the:

Options

A. Stroma
B. Thylakoid
C. Mitochondrial matrix
D. Cytoplasm

Answer

To solve the question regarding where ATP is produced during photosynthesis using sunlight, we can follow these steps:

### Step-by-Step Solution:

1. **Understand Photosynthesis**: Photosynthesis occurs in two main stages: the light-dependent reactions and the light-independent reactions (Calvin cycle). The light-dependent reactions are where ATP is produced.

2. **Identify the Structures Involved**: The key structures involved in the light-dependent reactions are the thylakoids and the stroma of the chloroplasts.

3. **Focus on Thylakoids**: The thylakoids are membrane-bound structures within chloroplasts that contain chlorophyll and are the site of the light-dependent reactions.

4. **ATP Production Mechanism**: During the light-dependent reactions, sunlight is absorbed by chlorophyll, which energizes electrons. This leads to the splitting of water molecules (photolysis), releasing oxygen and creating a proton gradient across the thylakoid membrane.

5. **ATP Synthesis**: The energy from the proton gradient is used by ATP synthase, an enzyme located in the thylakoid membrane, to convert ADP and inorganic phosphate (Pi) into ATP.

6. **Conclusion**: Therefore, the production of ATP using sunlight occurs in the thylakoid lumen of the chloroplasts.

### Final Answer:
The reaction in photosynthesis where ATP is produced using sunlight occurs in the **thylakoid lumen**.