During photophosphorylation in accordance with lysis of water the following reaction takes place:
`H_2O+H_3PO_4+ADP+NADPoverset("light")rarrNADPH_2+ATP+'X'.` where X is

Options

A. `1/2 O_2`
B. `H_2O`
C. `O_2`
D. `H^+`

Answer

To solve the question regarding the reaction during photophosphorylation and identify what 'X' is, we can break down the process step by step:

### Step-by-Step Solution:

1. **Understand the Reaction**: The given reaction is:
\[ H_2O + H_3PO_4 + ADP + NADP \overset{\text{light}}{\rightarrow} NADPH_2 + ATP + 'X' \]
We need to identify what 'X' represents in this context.

2. **Identify Components**:
- **H2O**: Water, which is involved in the process of photolysis (splitting of water).
- **H3PO4**: Phosphoric acid, which provides phosphate groups.
- **ADP**: Adenosine diphosphate, which is phosphorylated to form ATP.
- **NADP**: Nicotinamide adenine dinucleotide phosphate, which is reduced to NADPH.

3. **Photolysis of Water**: In the presence of light, water undergoes photolysis. This process can be summarized as:
\[ 2H_2O \rightarrow 4H^+ + 4e^- + O_2 \]
This means that water splits into hydrogen ions (protons), electrons, and oxygen.

4. **Formation of NADPH and ATP**:
- The electrons released from the photolysis of water are used to reduce NADP to NADPH.
- The energy from light is also used to convert ADP and inorganic phosphate (from H3PO4) into ATP.

5. **Identify 'X'**:
- From the photolysis of water, we see that oxygen is produced as a byproduct.
- Specifically, for every two molecules of water, one molecule of oxygen (O2) is produced. Since the equation is simplified, 'X' corresponds to half of the O2 produced in the reaction.

6. **Conclusion**: Therefore, 'X' in the reaction is:
\[ X = \frac{1}{2} O_2 \]

### Final Answer:
X is \( \frac{1}{2} O_2 \).

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