The correct answer is option 4, Haemoglobin. Haemoglobin is the respiratory pigment found in humans. It is a protein molecule found in red blood cells and is responsible for carrying oxygen from the lungs to the rest of the body. When oxygen binds to haemoglobin, it forms oxyhemoglobin. When oxygen is released from haemoglobin, it forms deoxyhemoglobin. This oxygen-binding and releasing process allows for efficient oxygen transport throughout the body.

Option 1, Haemocyanin, is the respiratory pigment found in some invertebrates, such as crustaceans and mollusks.

Option 2, Haemoerythrin, is also a respiratory pigment found in some marine invertebrates, such as polychaete worms and sipunculid worms.

Option 3, b-Carotene, is not a respiratory pigment, but rather a pigment found in plants that gives them their orange color.

Therefore, the correct answer is haemoglobin.