Which of the following is a set of animals in which all show external…

Concept: Fertilization is the fusion of male and female gametes to form a zygote. In internal fertilization the gametes fuse inside the female's body — typical of terrestrial animals such as birds, reptiles, and insects, since dry surroundings make gamete survival outside the body difficult. In external fertilization the gametes are released into the surrounding medium, almost always water, and fuse outside the body — typical of many aquatic animals such as fish, amphibians, and echinoderms.

Application: Hens (birds), lizards (reptiles), and butterflies (insects) all reproduce through internal fertilization. Frogs (amphibians) release eggs and sperm into water, where fertilization takes place outside the body. Fish typically release eggs and milt into water for external fertilization. Starfish (echinoderms) release eggs and sperm directly into seawater, where fertilization occurs externally. So among the four groups, only the set of frogs, fish, and starfish has every member fertilizing externally.

Contrast with the other options:

• Hens, lizards, butterflies — all three fertilize internally, so none of them fits an external-fertilization set.

• Lizards, butterflies, frogs — lizards and butterflies fertilize internally, so the group is mixed even though frogs fertilize externally.

• Butterflies, frogs, fish — butterflies fertilize internally, so the group is mixed even though frogs and fish fertilize externally.

• Frogs, fish, starfish — every member releases gametes into water and fertilizes externally, so this group satisfies the condition.

Cross-check: Grouping the animals by habitat and reproductive mode gives the same result — terrestrial egg-layers (birds, reptiles) and insects fertilize internally to protect gametes from drying out, while the fully aquatic/semi-aquatic group here releases gametes into water for external fertilization. This is confirmed by the official CTET (January 2024, Paper 2) answer key.