This about Class Amphibia is correct

(i) fertilization is internal

(ii) respiration is through gills only

(iii) body is divisible into head and trunk

(iv) heart is two chambered – one ventricle and one auricle

The correct option is only (iii).

Let us analyze each statement step-by-step to understand why only statement (iii) is correct regarding Class Amphibia:

Statement (i): Fertilization is internal (Incorrect)
In most amphibians, such as frogs and toads, fertilization is external. The female releases eggs into the water, and the male releases sperm over them to fertilize them externally. Hence, statement (i) is incorrect.

Statement (ii): Respiration is through gills only (Incorrect)
Amphibians exhibit multiple modes of respiration depending on their life stage and environment. While larval amphibians (like tadpoles) respire through gills, adult amphibians typically respire using lungs (pulmonary respiration) and their moist skin (cutaneous respiration). Some adults may also use the buccopharyngeal cavity. Therefore, respiration is not through gills only, making statement (ii) incorrect.

Statement (iii): Body is divisible into head and trunk (Correct)
The body of most amphibians (such as frogs) is structurally divided into two main regions: the head and the trunk. A neck is absent, which helps them streamline for swimming and jumping. Tail may be present in some forms (like salamanders) but the general body plan is divided into head and trunk. Thus, statement (iii) is correct.

Statement (iv): Heart is two chambered – one ventricle and one auricle (Incorrect)
Amphibians possess a three-chambered heart, which consists of two auricles (atria) and one ventricle. A two-chambered heart is characteristic of fishes, not amphibians. Hence, statement (iv) is incorrect.

Since only statement (iii) is correct, the correct choice is only (iii).