< b="" />Introduction: < />
In eukaryotes, the process of gene expression involves several steps, including transcription and translation. During transcription, an RNA molecule is synthesized from a DNA template. However, this initial RNA molecule, called pre-mRNA, undergoes several modifications before it is transported to the cytoplasm for translation.

< b="" />Pre-mRNA Processing: < />
Pre-mRNA processing involves several modifications, including the removal of non-coding regions (introns) and the addition of specific sequences to the mRNA molecule. These modifications are crucial for the production of mature mRNA that can be effectively translated into protein.

< b="" />Removal of Introns: < />
In eukaryotes, most genes contain introns, which are non-coding regions within the DNA sequence. These introns are transcribed into the pre-mRNA molecule along with the coding regions (exons). However, before the pre-mRNA can be transported to the cytoplasm, the introns must be removed through a process called splicing. Splicing is carried out by a complex called the spliceosome, which recognizes specific sequences at the boundaries between introns and exons. The introns are then removed, and the exons are joined together to form the mature mRNA molecule.

< b="" />Addition of 5' Cap: < />
After the removal of introns, the pre-mRNA undergoes further modifications. One of these modifications is the addition of a 5' cap. The 5' cap is a modified guanine nucleotide that is added to the 5' end of the mRNA molecule. This cap plays a crucial role in several cellular processes, including mRNA stability, transport, and translation initiation. The 5' cap also helps protect the mRNA from degradation by exonucleases.

< b="" />Addition of 3' Poly A Tail: < />
Another modification that occurs during pre-mRNA processing is the addition of a 3' poly A tail. The poly A tail is a string of adenine nucleotides added to the 3' end of the mRNA molecule. This modification also plays a role in mRNA stability and transport. Additionally, the poly A tail is involved in the process of translation initiation, as it interacts with specific proteins involved in ribosome binding.

< b="" />Conclusion: < />
In eukaryotes, the removal of introns is the primary modification that occurs during pre-mRNA processing. Additionally, the mRNA molecule undergoes the addition of a 5' cap and a 3' poly A tail. These modifications are crucial for the production of mature mRNA that can be transported to the cytoplasm for translation. Therefore, the correct answer to the question is (1) Intron.

(1)Intron is correct answer.