In the following statements, one word per statement is underlined. This word can be changed to obtain the correct statement. In which one it should not be changed?

Options

A. In the living world `ul("all")` organisms have DNA as the genetic material which can be transmitted from one generation to another.
B. Purine pyrimidine ratio in Ribose Nucleic Acid can `ul("never")` be equal to 1.
C. The 3rd carbon atom and the 5th carbon atom of `ul("all")`nucleotides in DNA are involved in the formation of phosphodiester bond.
D. Monocyclic nitrogen bases `ul("always")` form weak hydrogen bonds with dicyclic nitrogen bases in B - DNA.

Answer

To solve the question, we need to analyze each statement and identify which underlined word, if changed, would alter the meaning of the statement. We are looking for the statement that should not have its underlined word changed.

### Step-by-Step Solution:

1. **Statement Analysis**:
- **Statement 1**: "In the living world, all organisms have **DNA** as a genetic material which can be transmitted from one generation to another."
- If we change "DNA" to "RNA," the meaning changes, as RNA is not the genetic material in all organisms.

- **Statement 2**: "Purine **perimeter** ratio in ribose nucleic acid can never be equal to 1."
- If we change "perimeter" to "purine," the meaning changes because it would no longer refer to the correct ratio in nucleic acids.

- **Statement 3**: "The **third** carbon and the fifth carbon of all nucleotides."
- If we change "third" to "second," the meaning changes, as it would refer to a different carbon in the nucleotide structure.

- **Statement 4**: "Monocyclic nitrogen bases **always** form weak bonds."
- If we change "always" to "sometimes," the meaning changes, as it would imply that weak bonds are not consistently formed.

2. **Identifying the Correct Statement**:
- After analyzing all statements, we see that changing the underlined word in **Statement 2** does not alter the fundamental meaning of the statement. It remains true that the purine perimeter ratio can be equal to 1, as it is a factual statement about nucleic acids.

3. **Conclusion**:
- The statement that should not be changed is **Statement 2**.

### Final Answer:
- The word in **Statement 2** should not be changed.