Dreadful is something terrible, appalling, fearful. In nature, dreadful limits would be set to the extent wrong has been done; so a negative connotation would characterize the blank. Of all the options, (2) and (4) connotates negative meanings. “Dissimulation” is to hide (one's feelings, motives, etc) by pretense; which will lead a person into wrong doing. Therefore, it fits our prediction and is the answer.
“Solecism” is a violation of good manner; breach of etiquette; which would not set dreadful limits in nature, hence ruled out. Hence, (2) is the answer.