Explanation:

- Crocodiles have a unique heart structure compared to most reptiles.

- Option:2, four :

- Crocodiles have a four-chambered heart, similar to birds and mammals.

- This helps in achieving efficient separation of oxygenated and deoxygenated blood.

- Option:1, two:

- Incorrect; two-chambered hearts are characteristic of fish.

- Option:3, three:

- Most reptiles, like lizards and snakes, have three-chambered hearts, not crocodiles.

- Option:4, single:

- Incorrect; single-chambered hearts are not found in vertebrates.