when transcription occurs in eukaryotic cells, a dna strand is copied to an mrna strand that contains introns and exons. which of the two is needed for the production of proteins, and why?
introns because they are coding sequences.
introns because they are non-coding sequences.
exons because they are non-coding sequences.
exons because they are coding sequences.

The correct answer is Exon because they are coding sequence.

Explanation:

The primary mRNA transcript that formed from DNA during transcription contain both coding and non coding sequence.The coding sequence is called exon whereas the non coding sequence is termed as intron.

          As introns are non coding sequence they get spliced from the primary mRNA transcript resulting in the formation of mature mRNA containing only coding sequence or exons.

         The exon containing mRNA then enters into the cytoplasm to initiate translation or protein biosynthesis.

b is the best answer for this question.