Q.Which one of the following sets of animals share a four chambered heart?

The correct option is (B) Crocodiles, Birds, Mammals.

• Among reptiles, the heart is usually three-chambered, but crocodiles are the exception with a fully four-chambered heart.
• Birds (class Aves) have a completely four-chambered heart.
• Mammals also have a four-chambered heart.
• Amphibians and most reptiles (other than crocodiles) have only a three-chambered heart, so options built on "Amphibian" or "Lizards/Turtles" cannot be correct.

Heart structure becomes progressively more complex across the vertebrate classes: fish have a two-chambered heart, amphibians a three-chambered heart, most reptiles a three-chambered heart, and birds and mammals a fully four-chambered heart.

• Amphibians always have a three-chambered heart (two auricles, one ventricle), so any set including "Amphibian" as a four-chambered example is wrong.
• Reptiles as a class usually have a three-chambered heart, with crocodiles being the specific exception that has evolved a complete four-chambered heart. Lizards and turtles, both reptiles other than crocodiles, remain three-chambered, which rules out option (C).
• Birds always have a completely four-chambered heart, supporting their high metabolic demands as warm-blooded, flying animals.
• Mammals also always have a four-chambered heart, matching their warm-blooded physiology.

So the only combination where every member genuinely has a four-chambered heart is crocodiles (the reptilian exception), birds and mammals.

Method: Exception-first table building

Rather than trying to recall each option's heart-chamber count directly, build a small mental table of "default heart type per class," flag the ONE known exception, and use that exception to test the options.

Step 1 — lay out the class defaults: Fishes = two chambers (default, no exceptions taught). Amphibians = three chambers (default, no exceptions taught). Reptiles = three chambers (the DEFAULT for the class). Birds = four chambers (default, no exceptions). Mammals = four chambers (default, no exceptions).

Step 2 — flag the one exception explicitly: among reptiles, crocodiles break the class default and have evolved a full four-chambered heart, unlike lizards, turtles and other reptiles which stay three-chambered.

Step 3 — test each option against the table plus the exception:

• (a) Amphibian, Reptiles, Birds — amphibian is three-chambered (default), so this set already fails; discard.
• (c) Crocodiles, Lizards, Turtles — lizards and turtles are ordinary reptiles, so they stay three-chambered even though crocodiles are the exception; this set fails.
• (d) Lizards, Mammals, Birds — lizards are three-chambered (ordinary reptile default); this set fails.
• (b) Crocodiles, Birds, Mammals — crocodiles use the EXCEPTION (four-chambered), while birds and mammals use their own four-chambered DEFAULT. Every member of this set is genuinely four-chambered.

Building the table of defaults first, and treating the crocodile as a deliberately flagged exception rather than trying to remember it alongside every other reptile, makes it obvious which set is internally consistent.

Conclusion: Laying out each class's default heart-chamber count and specifically flagging crocodile as the one reptile exception reaches the same answer as direct recall — option (b), crocodiles, birds and mammals — while explaining precisely why lizards and turtles cannot join that set.