The denotation of a word is its dictionary definition.
"Lurid" means "vivid," but in an unpleasant way.
Something soothing has a calming effect; this is essentially the opposite of lurid. Invisible means literally "not visible" - more to do with senses than having a vividly unpleasant feeling. To be attentive is to be alert or aware, which does not fit our definition above. That leaves shocking, which is a feeling of unwelcome surprise or dismay; this is correct.
