An ion channel that opens when neurotransmitter binds to it is called a channel.

An ion channel that opens when neurotransmitter binds to it is called a ligand-gated channel. Ligand-gated channel is a group of transmembrane ion channel proteins which open to allow the passage of ions such as Na+, K+ through the membrane upon activation by a specific chemical such as a neurotransmitter.

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c. is the correct answer