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, we need to analyze the components involved in the reaction and what occurs during the process.

### Step-by-Step Solution:

1. **Identify the Components of the Reaction**:
The given reaction is:
\[ H_2O + H_3PO_4 + ADP + NADP \overset{\text{light}}{\rightarrow} NADPH_2 + ATP + 'X' \]
Here, we have water (H2O), phosphoric acid (H3PO4), adenosine diphosphate (ADP), and nicotinamide adenine dinucleotide phosphate (NADP) as reactants.

2. **Understand the Process of Photophosphorylation**:
Photophosphorylation is a process that occurs during photosynthesis where light energy is used to convert ADP and inorganic phosphate (from H3PO4) into ATP. Simultaneously, NADP is reduced to NADPH.

3. **Analyze the Role of Water**:
In the process of photophosphorylation, water undergoes photolysis (light-induced breakdown). This reaction produces oxygen (O2), protons (H+), and electrons (e-). The overall reaction for the photolysis of water can be summarized as:
\[ 2 H_2O \rightarrow 4 H^+ + 4 e^- + O_2 \]
This means that for every two molecules of water, one molecule of oxygen is released.

4. **Determine the Value of 'X'**:
In the original reaction, when water is split, it produces oxygen. In the context of the reaction provided, 'X' represents the product of the photolysis of water, which is half of the molecular oxygen produced. Therefore, since the reaction involves the splitting of water, 'X' is:
\[ X = \frac{1}{2} O_2 \]

5. **Final Answer**:
Thus, the value of 'X' in the reaction is:
\[ X = \frac{1}{2} O_2 \]