Which of the following is true about base pairing in nucleic acids?

In nucleic acids, specifically in RNA, adenine (A) pairs with uracil (U). This is in contrast to DNA, where adenine pairs with thymine (T). The pairing of A with U is crucial for the proper encoding and decoding of genetic information during processes such as transcription, where RNA is synthesized from a DNA template.

In RNA, uracil replaces thymine, and since both adenine and uracil are single-ring structures, they fit together in a complementary and stable manner, facilitating the formation of the nucleic acid structure. This accurate base pairing is essential for maintaining the fidelity of genetic information, allowing for the correct synthesis of proteins and other functional molecules in the cell.

The other options do not represent accurate base pairing rules: guanine (G) does not pair with adenine (A), cytosine (C) does not pair with thymine (T), and thymine (T) does not pair with cytosine (C). Understanding the complementary pairings is fundamental in genetics and molecular biology.