**Explanation:**

Meiosis is the process of cell division that produces gametes (sperm and egg cells) for sexual reproduction. It involves two rounds of cell division, known as Meiosis I and Meiosis II. Meiosis II is the second round of division that follows Meiosis I. In Meiosis II, the two daughter cells produced in Meiosis I divide further to produce four haploid cells.

The purpose of Meiosis II is to separate the sister chromatids that were formed during Meiosis I. Each chromosome in the cell consists of two sister chromatids held together by a centromere. The separation of these sister chromatids ensures that each of the resulting haploid cells receives one copy of each chromosome.

Here is a detailed explanation of the options provided:

**a) Separation of sex chromosomes:**
Sex chromosomes, such as the X and Y chromosomes in humans, determine the sex of an individual. During Meiosis II, the sex chromosomes do not separate. Instead, they separate during Meiosis I.

**b) Synthesis of DNA and centromere:**
DNA synthesis occurs during the interphase before Meiosis I. The centromere is the region of the chromosome that holds the sister chromatids together. It is not synthesized during Meiosis II.

**c) Separation of homologous chromosomes:**
The separation of homologous chromosomes occurs during Meiosis I, not Meiosis II. In Meiosis I, homologous chromosomes pair up and separate, resulting in two daughter cells with a haploid set of chromosomes.

**d) Separation of chromatids:**
The correct answer is option 'd'. During Meiosis II, the sister chromatids separate from each other. This separation ensures that each of the resulting haploid cells receives one copy of each chromosome.

In summary, Meiosis II performs the separation of chromatids, ensuring that each haploid cell receives a complete set of chromosomes.