Answer: 2. Dopamine.
Dopamine is a neurotransmitter that is connected with bodily functions like movement, learning, attention, and mood and is the major substance that facilitates the feeling of pleasure and the thrill that comes with receiving rewards. The distribution of dopamine throughout the body leads to the formation of addictions.
Neurotransmitters are substances that are tasked with the function of transmitting nerve signals between two neurons across a synapse.