Statement A: In brown algae zoospores and gametes produced from one thallus are genetically similar.
Statement B: Brown algae are rarely present in fresh water usually present in marine (salt) water and brackish water.

Statement A is true. In brown algae, the zoospores and gametes produced by a single thallus (body) are often genetically similar because they are both haploid and are derived from the same reproductive structures. This is a common feature in the life cycle of many brown algae, where both zoospores and gametes are produced during different stages of the life cycle.

Statement B is also true.  Brown algae, which are a type of seaweed, are primarily marine organisms. While some species can tolerate brackish water (a mixture of saltwater and freshwater), they are indeed rarely found in purely freshwater environments. Brown algae are more commonly associated with marine or coastal habitats where they thrive in saltwater conditions. Freshwater algae are typically a different group, such as green algae.