The sequences of four DNA molecules are given below:
i. TATATATATATATA
ATATATATATATAT
ii. TTTCCCGGGAAA
AAAGGGCCCTTT
iii. TTGCGTTGCCC
AACGCAACGGG
iv. GCCGGATCCGGC
CGGCCTAGGCCG
Which one of these DNA moelcules will have the highest melting temperature `(T_m)`?

Options

A. i
B. ii
C. iii
D. iv

Explanation

To determine which of the four DNA molecules has the highest melting temperature (T_m), we need to analyze the sequences based on their GC content. The melting temperature of DNA is influenced by the number of hydrogen bonds between the base pairs: adenine (A) pairs with thymine (T) via two hydrogen bonds, while guanine (G) pairs with cytosine (C) via three hydrogen bonds. Therefore, a higher GC content in a DNA molecule generally correlates with a higher melting temperature.

### Step-by-Step Solution:

1. **Identify the Sequences**:
- i. TATATATATATATA / ATATATATATATAT
- ii. TTTCCCGGGAAA / AAAGGGCCCTTT
- iii. TTGCGTTGCCC / AACGCAACGGG
- iv. GCCGGATCCGGC / CGGCCTAGGCCG

2. **Count the GC Content**:
- For each sequence, count the number of G and C bases.
- **i**: A=8, T=6, G=0, C=0 → GC content = 0
- **ii**: A=6, T=3, G=6, C=3 → GC content = 9
- **iii**: A=4, T=3, G=4, C=3 → GC content = 7
- **iv**: A=3, T=1, G=6, C=5 → GC content = 11

3. **Determine the Highest GC Content**:
- From the counts:
- i: GC = 0
- ii: GC = 9
- iii: GC = 7
- iv: GC = 11
- The sequence with the highest GC content is **iv** with 11 GC pairs.

4. **Conclusion**:
- Since the melting temperature (T_m) is higher for sequences with more GC pairs, the DNA molecule with the highest melting temperature is **iv. GCCGGATCCGGC / CGGCCTAGGCCG**.

### Final Answer:
The DNA molecule with the highest melting temperature is **iv**.