Assertion: Cephalisation is advantageous to an animal.
Reason: Cephalisation improves the appearance of an animal.
A. Both assertion and reason are correct and reason is the correct explanation of the assertion
B. Both assertion and reason are correct but reason is not the correct explanation of the assertion
C. Assertion is correct but reason is incorrect
D. Both assertion and reason are incorrect

Hint: Cephalisation is an evolutionary trend in which nervous tissue, sensory organs and other parts of the body are concentrated at the front end of the body and formed into a distinct head and brain. Cephalisation is seen in mainly three groups- arthropods, vertebrates and some molluscs under the kingdom Animalia.

Complete answer-
Cephalisation happens over many generations. It provides many advantages to an animal than non-cephalized ones.
The main advantage of cephalisation is the evolution of complex neural systems in cephalized animals. This is because there is a formation of the distinct heads in these animals which controls the overall functioning of the body. With time, they develop higher intelligence.
The second advantage of cephalisation is that it results in the closeness of the mouth towards the brain and other sensory organs. The cephalized animals can easily sense the surrounding environment. It helps in the quick search of prey and other information by sensing the environment.
The third advantage of cephalisation is the evolution of forward-facing organisms due to the concentration of sensory organs at the front end of the organism. This helps the organism in easy search of food and habitat. It allows the organism to easily identify the environment and avoid danger.

Thus the answer to the above question is Assertion is true but reason is false as cephalisation has many advantages to an animal due to the formation of a distinct head but it does not improve the appearance of the animal.

Note:
The cephalisation is related to bilateral symmetry. The organisms having radial symmetry lack cephalisation. Echinoderms and cnidarians are the groups of animals in which cephalisation is not found. The absence of cephalisation does not mean that they are less evolved. With time, they adapted themselves to different kinds of environmental conditions.