Q.Match the following a. Amphibia / i. Air bladder
b. Mammals / ii. Cartilaginous notochord
c. Chondrichthyes / iii. Mammary glands
d. Ostichthyes / iv. Pneumatic bones
e. Cyclostomata / v. Dual habitat
f. Aves / vi. Sucking and circular mouth without jaws.

a. Amphibia — v. Dual habitat.

b. Mammals — iii. Mammary glands.

c. Chondrichthyes — ii. Cartilaginous notochord (cartilaginous endoskeleton, notochord persists).

d. Osteichthyes — i. Air bladder.

e. Cyclostomata — vi. Sucking and circular mouth without jaws. …

Every vertebrate class carries one especially defining structural or ecological feature.

• a. Amphibia live in both aquatic and terrestrial habitats, so its name itself reflects this dual habitat.
• b. Mammals are uniquely marked by mammary glands, through which mothers nourish their young.
• c. Chondrichthyes have an entirely cartilaginous internal skeleton, and their notochord persists throughout life, matching a cartilaginous notochord/endoskeleton. …

Method: Elimination by exclusive/unique markers

Instead of matching each class to a feature directly, first identify which of the six listed features is UNIQUE to only one class (and could not plausibly belong to any other), assign those first, and let the remaining pairs fall out by elimination.

Find the exclusive markers first:

• "Mammary glands" is uniquely and exclusively a mammalian feature — no other vertebrate class has it. Assign immediately: Mammals-iii.
• "Sucking and circular mouth without jaws" is uniquely a Cyclostomata feature (the only jawless class in the list) — no other class listed has a jawless mouth. Assign immediately: Cyclostomata-vi.
• "Pneumatic bones" is a flight-specific adaptation exclusive to birds among this list — mammals, reptiles and amphibians don't have hollow, air-filled bones. Assign immediately: Aves-iv.

With three pairs already fixed, use elimination for the remaining three:

• "Air bladder" is the buoyancy-regulating organ specific to bony fishes (Osteichthyes) — since Cyclostomata, Mammals and Aves are already assigned elsewhere, and cartilaginous fishes (Chondrichthyes) are explicitly described as LACKING an air bladder (forcing them to swim constantly), the air bladder can only belong to Osteichthyes. Assign: Osteichthyes-i.
• "Cartilaginous notochord" (a persistent, cartilage-based internal skeleton with the notochord retained) fits Chondrichthyes, the one remaining fish class after Osteichthyes is assigned. Assign: Chondrichthyes-ii. …