Given below is one of the strands of a DNA segment :

(a) Write its complementary strand.

(b) Write a possible RNA strand that can be transcribed from the above DNA molecule formed.

Based on the provided images, the correct answers are:
(a) Complementary DNA strand: 5′-ATGCATGCATGCATGC-3′
(b) Transcribed RNA strand: 5′-AUGCAUGCAUGCAUGC-3′

Step-by-Step Explanation:

1. Analysis of the Given DNA Strand (from Image 0):
The first image shows a single strand of a DNA segment with its polarity marked as:
3′-TACGTACGTACGTACG-5′
An arrow pointing to the right is visible under the middle nucleotides (specifically under the "GT" sequence).

2. Part (a): Writing the Complementary DNA Strand (from Image 1):
DNA molecules consist of two antiparallel strands held together by complementary base pairing. To find the complementary strand, we apply Watson-Crick base-pairing rules:
• Adenine (A) always pairs with Thymine (T) via two hydrogen bonds.
• Cytosine (C) always pairs with Guanine (G) via three hydrogen bonds.
• The polarity is reversed (the 3′ end of one strand aligns with the 5′ end of the other).

Let's pair each base of the given 3′-TACGTACGTACGTACG-5′ strand:
• T (at 3′) pairs with A (at 5′)
• A pairs with T
• C pairs with G
• G pairs with C
Repeating this sequence four times yields:
Complementary Strand: 5′-ATGCATGCATGCATGC-3′
This matches the second image, which explicitly labels this sequence with a rightward arrow and the marking (polarity = 1/2 , nucleotide sequence = 1/2).

3. Part (b): Writing the Transcribed RNA Strand (from Image 2):
During transcription, an RNA strand is synthesized using the template DNA strand (3′ to 5′ direction) to generate a complementary RNA strand (5′ to 3′ direction).
The base pairing rules for RNA synthesis are identical to DNA replication, except that RNA contains Uracil (U) instead of Thymine (T):
• Thymine (T) on the DNA template pairs with Adenine (A) in RNA.
• Adenine (A) on the DNA template pairs with Uracil (U) in RNA.
• Cytosine (C) on the DNA template pairs with Guanine (G) in RNA.
• Guanine (G) on the DNA template pairs with Cytosine (C) in RNA.

Using the template strand 3′-TACGTACGTACGTACG-5′:
• T (at 3′) transcribes to A (at 5′)
• A transcribes to U
• C transcribes to G
• G transcribes to C
Repeating this sequence four times yields the RNA strand:
Transcribed RNA Strand: 5′-AUGCAUGCAUGCAUGC-3′
This matches the third image, which shows this sequence with a rightward arrow and the marking (polarity = 1/2 , nucleotide sequence = 1/2).