Every body laughed at the puerility of his statement

Answer: Option B

Inaccuracy : the quality or state of not being accurate.
Childishness : of, like, or appropriate to a child.
Insincerity : the quality of not expressing genuine feelings.
Falsehood : the state of being untrue.
Puerility : childishly silly and immature.

Synonym of Puerility is Childishness