Explanation:

Second option is correct.

The oxygen carrying molecule in the blood of humans is known as Hemoglobin.

Hemoglobin (Hb or Hgb) is a protein in red blood cells that carries oxygen throughout the body. In many cases, a low hemoglobin count is only slightly lower than normal and doesn't affect how you feel. If it gets more severe and causes symptoms, your low hemoglobin count may indicate you have anemia.