Hyperacusis in Bell's palsy is due to the paralysis of the following muscle:

(d) Stapedius(Ref. Cummings, 6th ed., 2620)Hyperacusis is normal sounds perceived as abnormally loud. This is due to loss of Stapedial reflex. In Bell's palsy this is due to paralysis of the facial nerve which supplies the stapedius.Tensor tympani which also helps in protecting the ear from loud noise, is supplied by the mandibular nerve.The other muscles in the options are not involved in hyperacusis.