In the DNA molecule :

Options

A. Proportion of adenine in relation to thymine varies with organism
B. There are two strands which run antiparallel — one in 5’-3’ direction and other in 3’-5’ direction
C. The total amount of purine nucleotides and pyrimidine nucleotides is not always equal
D. There are two strands which run parallel in the 5’-3’ direction

Answer

### Step-by-Step Solution:

1. **Understanding the Structure of DNA**:
- DNA (Deoxyribonucleic Acid) is composed of two strands that form a double helix. Each strand is made up of nucleotides, which consist of a sugar, a phosphate group, and a nitrogenous base.

2. **Analyzing the First Statement**:
- The statement claims that the proportion of Adenine (A) varies with Thymine (T) in different organisms.
- According to Chargaff's rules, in a double-stranded DNA molecule, the amount of Adenine is always equal to Thymine (A = T). Therefore, this statement is **incorrect**.

3. **Analyzing the Second Statement**:
- The statement mentions that the two strands of DNA run anti-parallel, with one strand running in the 5' to 3' direction and the other in the 3' to 5' direction.
- This is a true characteristic of DNA structure. Hence, this statement is **correct**.

4. **Analyzing the Third Statement**:
- The statement asserts that the total amount of Purine nucleotides is not equal to the total amount of Pyrimidine nucleotides.
- However, it is known that Purines (Adenine and Guanine) pair with Pyrimidines (Thymine and Cytosine) through hydrogen bonds, leading to equal amounts of Purines and Pyrimidines (A + G = T + C). Thus, this statement is **incorrect**.

5. **Analyzing the Fourth Statement**:
- The statement claims that the two strands run parallel in the 5' to 3' direction.
- This is false because the strands are anti-parallel, meaning they run in opposite directions. Thus, this statement is also **incorrect**.

6. **Conclusion**:
- The only correct statement among the provided options is the second statement regarding the anti-parallel nature of the DNA strands. Therefore, the correct answer is option B.