Final answer:
The nurse should inform the client that succinylcholine prevents muscle movements during the seizure induced by ECT.
Step-by-step explanation:
The nurse should respond to the client's question by choosing option C, "It prevents muscle movements during the seizure induced by ECT." Succinylcholine is a medication that belongs to the class of neuromuscular blocking agents and is used to induce muscle relaxation and paralysis during electroconvulsive therapy (ECT). ECT involves the administration of an electric current to the brain to produce a controlled seizure, and succinylcholine helps prevent muscle movements during this procedure.