The ratio of the number of ketonic groups in cytosine, thymine and uracil is

Options

A. `1:2:2`
B. `2:1:2`
C. `2:2:1`
D. `1:1:1`

Answer

To determine the ratio of the number of ketonic groups in cytosine, thymine, and uracil, we can follow these steps:

### Step 1: Identify the structure of each molecule
- **Cytosine**: A pyrimidine base with the chemical formula C4H5N3O.
- **Thymine**: A pyrimidine base with the chemical formula C5H6N2O2.
- **Uracil**: A pyrimidine base with the chemical formula C4H4N2O2.

### Step 2: Analyze the ketonic groups in each base
- **Cytosine**: Contains **1 ketonic group** (C=O).
- **Thymine**: Contains **2 ketonic groups** (two C=O).
- **Uracil**: Contains **2 ketonic groups** (two C=O).

### Step 3: Count the ketonic groups
- Cytosine: 1 ketonic group
- Thymine: 2 ketonic groups
- Uracil: 2 ketonic groups

### Step 4: Establish the ratio
The ratio of ketonic groups in cytosine, thymine, and uracil can be expressed as:
- Cytosine : Thymine : Uracil = 1 : 2 : 2

### Conclusion
The ratio of the number of ketonic groups in cytosine, thymine, and uracil is **1 : 2 : 2**. Therefore, the correct answer is option A.

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