**The first stable intermediate product of photosynthesis is phosphoglyceric acid (PGA).**

**Explanation:**

Photosynthesis is the process by which green plants, algae, and some bacteria convert light energy from the sun into chemical energy in the form of glucose. It occurs in the chloroplasts of plant cells.

During photosynthesis, a series of complex reactions take place, which can be divided into two main stages: the light-dependent reactions and the light-independent reactions (also known as the Calvin cycle).

The light-dependent reactions occur in the thylakoid membranes of the chloroplasts and involve the conversion of light energy into chemical energy in the form of ATP and NADPH. These energy-rich molecules are then used in the light-independent reactions.

The light-independent reactions, also known as the Calvin cycle, occur in the stroma of the chloroplasts. These reactions involve the fixation of carbon dioxide (CO2) and the synthesis of glucose.

**The Calvin cycle can be summarized into three main stages:**

1. **Carbon Fixation:**
- The enzyme RuBisCO (ribulose-1,5-bisphosphate carboxylase/oxygenase) catalyzes the reaction between carbon dioxide (CO2) and a 5-carbon compound called ribulose-1,5-bisphosphate (RuBP).
- This reaction results in the formation of an unstable 6-carbon compound, which quickly breaks down into two molecules of 3-phosphoglycerate (PGA).
- PGA is the first stable intermediate product of photosynthesis.

2. **Reduction:**
- Each molecule of PGA is then converted into a molecule of glyceraldehyde-3-phosphate (G3P) through a series of reactions.
- This conversion requires ATP and NADPH, which were produced during the light-dependent reactions.
- Some of the G3P molecules are used to regenerate RuBP, while others are used to produce glucose and other organic compounds.

3. **Regeneration:**
- The remaining G3P molecules are rearranged and combined to regenerate RuBP, which can then react with more carbon dioxide in the carbon fixation stage.
- This regeneration step is essential to sustain the Calvin cycle and continue the synthesis of glucose.

In summary, phosphoglyceric acid (PGA) is the first stable intermediate product of photosynthesis. It is formed through the carbon fixation stage of the Calvin cycle, where carbon dioxide is fixed and converted into PGA. This molecule is then further processed and converted into glyceraldehyde-3-phosphate (G3P), which is used to produce glucose and regenerate the starting compound, ribulose-1,5-bisphosphate (RuBP).

The first stable intermediate product of photosynthesis is phosphoglyceric acid so option c is correct