Acetylcholine receptors on skeletal muscles are described as being ionotropic receptors because

Binding of acetylcholine to the receptor protein converts the protein to an open ion channel

Explanation:

Ionotropic receptors are those receptors that have binding sites for their messenger ligands and also have the capacity to alter shape enough to become an open ion channel,and thus allowing an increase in cross-membrane traffic of ions, thus altering the membrane potential.Therefore, Acetylcholine receptors on skeletal muscles are described as being ionotropic receptors because the binding of acetylcholine to the receptor protein converts the protein to an open ion channel