ASSERTION: Brown Algae varies from olive green to brown in colour.
REASON: Fucoxanthin is responsible for colour variation in brown algae
A. Both assertion and reason are correct and Reason is the correct explanation for assertion.
B. Both assertion and reason are correct but reason is not the correct explanation of assertion.
C. Assertion is correct but Reason is incorrect.
D. Both assertion and reason are incorrect.

Hint: Algae are photosynthetic species that have photosynthetic pigments, such as chlorophyll. However, they lack the true roots, stems and leaves that are characteristic of vascular plants. Some are single-celled, while others are multicellular. Colonies can also be formed.

Complete Answer:
- Brown algae (Phaeophyceae population), a class of around 1,500 Chlorophyte division algae species, abundant in cold waters along the continental coast. Depending on the proportion of brown pigments (fucoxanthin) to green pigments (chlorophyll), the colour of the species varies from dark brown to olive green.
- In temperate areas (Fucus, Ascophyllum) or floating freely (Sargassum), other brown algae can be found attached to rocky coasts. Freshwater species are uncommon. By asexual and sexual reproduction, brown algae multiply; both the motile zoospores and gametes have two unequal flagella.
- In certain seaweed species, there are gas-filled bladders (pneumatocysts) that hold photosynthetic sections of the algal thallus floating on or near the water's surface.

The correct Answer is option (A) Both assertion and reason are correct and reason is the correct explanation for assertion.

Note: Brown algae, once a major source of iodine and potash, is now a major source of algin, a colloidal gel used as a stabiliser in the baking and ice cream industries. Some plants are also used as fertilisers and others in East Asia and elsewhere are eaten as vegetables (e.g., laminaria).