Meiosis is primarily characterized by the separation of homologous chromosomes. Therefore, the correct answer is b) separation of homologous chromosomes.
During meiosis, a single diploid cell divides to form four haploid cells. This process consists of two sequential divisions: meiosis I and meiosis II. In meiosis I, homologous chromosomes are separated, leading to the production of two haploid cells, each with one chromosome from each homologous pair. In contrast, meiosis II focuses on the separation of sister chromatids.
The other statements are not accurate descriptions of meiosis as a whole. While chromosome replication occurs prior to meiosis during the S phase of the cell cycle, it is not a defining feature of meiosis itself. Similarly, haploid cells do not become diploid during meiosis; instead, they are formed as a result of the process. Thus, the most accurate description of meiosis involves the separation of homologous chromosomes.