Which one of the following molecules is used for cell signaling?

Nitric Oxide (NO) is a major signaling molecule in neurons and in the immune system, either acting within the cell in which it is produced or by penetrating cellmembranes to affect adjacent cells. Nitric oxide is generated from arginine by the action of nitric oxidesynthases (NOS) Ref guyton and hall textbook of medical physiology 12/e pg 29