In the basic classification of algae, which one of the following statements about Chlorophyceae, Phaeophyceae and Rhodophyceae is not correct?

Introduction / Context:
This question checks your knowledge of the basic taxonomic groups of algae and their common names based on pigment composition. Algae are often grouped into Chlorophyceae, Phaeophyceae, and Rhodophyceae, which are commonly known as green algae, brown algae, and red algae respectively. Identifying which statement incorrectly matches a group with its common name is a frequent task in botany based competitive exams.

Given Data / Assumptions:
- Three algal classes are involved: Chlorophyceae, Phaeophyceae, and Rhodophyceae. - Each option links one of these classes with a common colour based name. - Only one of the four statements is incorrect. - Standard school level botany classification is assumed.

Concept / Approach:
Chlorophyceae includes algae rich in chlorophyll a and b, giving them a bright green colour, so they are called green algae. Phaeophyceae contains brown algae, where fucoxanthin pigment gives a brown or olive green colour. Rhodophyceae includes red algae, where phycoerythrin pigment imparts a red colour. Therefore, statements linking Chlorophyceae with green algae, Phaeophyceae with brown algae, and Rhodophyceae with red algae are all correct. Any statement that mismatches these colours and classes will be incorrect. In the given options, the statement saying Phaeophyceae are commonly called red algae is wrong because red algae belong to Rhodophyceae, not Phaeophyceae.

Step-by-Step Solution:
Step 1: Recall that members of Chlorophyceae are green algae due to abundant chlorophyll and are usually bright green in colour. Step 2: Remember that members of Phaeophyceae are typically brown algae because of the presence of fucoxanthin pigment along with chlorophyll. Step 3: Recall that members of Rhodophyceae are red algae, with phycoerythrin giving a characteristic red shade. Step 4: Evaluate option A, which states that members of Chlorophyceae are commonly called green algae. This is correct. Step 5: Evaluate option C, which states that members of Rhodophyceae are commonly called red algae. This is also correct. Step 6: Evaluate option D, which states that members of Phaeophyceae are commonly called brown algae. This matches standard classification and is correct. Step 7: Evaluate option B, which states that members of Phaeophyceae are commonly called red algae. This mislabels Phaeophyceae and is therefore incorrect.

Verification / Alternative check:
A quick way to verify is to remember the colour codes: Chlorophyceae equals green, Phaeophyceae equals brown, and Rhodophyceae equals red. Textbooks use this classification consistently and often present tables comparing their pigments, stored food, and habitat. You will not find any standard reference that calls Phaeophyceae red algae. Cross checking with simple memory aids like green chlorophyceae, brown phaeophyceae, red rhodophyceae confirms that Phaeophyceae being labelled red algae is the incorrect statement.

Why Other Options Are Wrong (as incorrect choices):
Members of Chlorophyceae are commonly called green algae: This is correct, so it cannot be the answer to a not correct question. Members of Rhodophyceae are commonly called red algae: This is also correct and well established. Members of Phaeophyceae are commonly called brown algae: This is the correct pairing and is widely used in marine botany.

Common Pitfalls:
A frequent mistake is mixing up Phaeophyceae and Rhodophyceae because both include many marine species and have pigments other than chlorophyll. Students sometimes rely only on vague colour impressions from pictures rather than the exact pigment names. Another pitfall is to rush through and pick the first statement that looks unusual without systematically checking each option against the standard colour classification. Taking a moment to recall the three colour coded names helps avoid these errors.

Final Answer:
The statement that is not correct is: Members of Phaeophyceae are commonly called red algae.