The correct answer is option 1: Red blood cells. Haemoglobin is a protein that is responsible for carrying oxygen throughout the body. It is found within the red blood cells, which are the cells specifically designed to transport oxygen from the lungs to the different tissues and organs in the body. Red blood cells have a high concentration of haemoglobin, which gives them their characteristic red color.

Option 2, white blood cells, are part of the immune system and are responsible for fighting infections. They do not contain haemoglobin.

Option 3, platelets, are small cell fragments that help in blood clotting. They also do not contain haemoglobin.

Option 4, plasma, is the liquid component of blood that carries various substances, including nutrients, hormones, and waste products. It does not contain haemoglobin.

Therefore, the correct answer is option 1, red blood cells.