SCURRILOUS:

Answer: Option A

Ribald: Vile,despicable, dishonorable, disgusting.
Abusive: Outrageous, Offensive, Insulting.
Mitigate : Reduce, decrease, make something lessen.
Decent: respectable or moral behaviour.
SCURRILOUS: Making or spreading scandalous claims about someone with the intention of damaging their reputation.

Antonym of SCURRILOUS is Decent.