How many molecules of water are needed by a green plant to reduce 6 molecules of `CO_2` ?

Options

A. 6
B. 12
C. 24
D. One only

Answer

To determine how many molecules of water are needed by a green plant to reduce 6 molecules of CO2, we can refer to the process of photosynthesis. Here’s a step-by-step solution:

### Step 1: Understand the Photosynthesis Equation
Photosynthesis can be summarized by the following equation:
\[ 6CO_2 + 6H_2O \rightarrow C_6H_{12}O_6 + 6O_2 \]
This equation indicates that 6 molecules of carbon dioxide (CO2) and 6 molecules of water (H2O) are used to produce one molecule of glucose (C6H12O6) and 6 molecules of oxygen (O2).

### Step 2: Analyze the Requirement for Water
From the equation, we can see that for every 6 molecules of CO2 that are fixed (reduced), 6 molecules of water are also required.

### Step 3: Determine the Proportionality
Since the equation shows a 1:1 ratio between CO2 and H2O in the context of the number of molecules involved in the reaction, we can conclude that to reduce 6 molecules of CO2, the same number of water molecules is needed.

### Step 4: Conclusion
Thus, for the reduction of 6 molecules of CO2, the plant requires:
\[ 6 \text{ molecules of } H_2O \]

However, if we consider the complete reaction and the stoichiometry involved, we find that to produce glucose, the plant actually needs 12 molecules of water to fully utilize the 6 molecules of CO2.

### Final Answer
Therefore, the total number of water molecules needed to reduce 6 molecules of CO2 is:
\[ 12 \text{ molecules of } H_2O \]