Why do phospholipids form a bilayer in water?

The fatty acid tails are cluster together to form the phospholipid bilayer.

Explanation:

A phospholipid is an amphipathic molecule having a hydrophilic head and hydrophobic tail. Phospholipid consists of three components such as phosphate head, glycerol, and Fatty acid tails. The phosphate head is the water-loving side. It comes in contact with water. The fatty acid tail is a water-hating side. They cluster together and don't allow water to pass through them. Thus another phospholipid layer forms inside the cell forming a lipid bilayer. In the lipid bilayer, the middle layer is lipid tails while outer and inner are phosphate heads.

b would be the right answer

a tetrad is the foursome during meiosis made by two homologous chromosomes that have each already replicated into a pair of sister chromatids.