Ans. is 'a' i.e., Doxacuriimi o Among the given options, only doxacurium is long acting.SKELETAL MUSCLE RELAXANTSo Skeletal muscle relaxants are drugs that act peripherally at neuromuscular junction/muscle fiber itself or centrally in the cerebrospinal axis to reduce muscle tone.o The neuromuscular blocking agents are used primarily in conjunction with general anesthetics to provide muscle relaxation for surgery, while centrally acting muscle relaxants are used mainly for painful muscle spasms and spastic neurological conditions.Muscle relaxantsPeripherally acting Centrally' acting o Mephenesin congenersy Mephensiney Carisoprodoly Chlorzoxazoney Chlormezanoney Methocarbamolo Benzodiazepinesy Diazepamo GABA derivativesy Baclofeno Central a2 - agonisty TizanidineNeuromuscular blocking agentsDirectly acting agents o Dantrolene sodiumo QuinineNondepolarizing (competitive) blockersDepolarizing blockersa) Long-acting -d. tubocurarine. Pancuronium, Doxacurium, Pipecuroniumo Succinylcholineo Decamethoniumb) Intermediate-acting-- Vecuronium, Atracurium,cisatracurium, Rocuronium, Rapacuroniumc)Short-acting-Mivacuriumo Competitive (nondepolarizing) blockers are of two typesBenzylisoquinoline derivativesThis includes - d-TC, doxacurium, atracurium, cisatracurium, mivacurium, metocurine.These drugs have tendency to release histamine and to block autonomic ganglion.Amminio steroid derivativesThis include pancuronium, rocuronium, vecuronium, pipecuronium, rapacuronium.These drugs do not block autonomic ganglia and have minimal histamine releasing property.