A
Nitric oxide
B
Nitrous oxide
C
Nitrogen dioxide
D
Nitrogen pentoxide
Correct answer: (a) Nitric oxide
Explanation
- A
Nitric oxide
Nitric oxide. Endothelium-derived relaxing factor; dilates vessels.
- B
Nitrous oxide
Nitrous oxide. Anaesthetic (“laughing gas”), not the body’s dilator molecule.
- C
Nitrogen dioxide
Nitrogen dioxide. Pollutant, not a vasodilator hormone.
- D
Nitrogen pentoxide
Nitrogen pentoxide. Not a human signalling molecule.
Summary. Official key is (a) nitric oxide (NO). Vascular endothelium makes NO, which relaxes smooth muscle and increases blood flow. Nitrous oxide (N2O) is an anaesthetic. NO2 and N2O5 are not the endogenous dilator.