1 Serious:
Absurd
He asked absurd questions in the classroom.
2 Scarce
Plentiful
Sita has plentiful clothes.
3 Idle
Busy
I am busy so I can't make it today.
4 Agree
Disagree
They did not like the plan so they disagree.
5 Create
Destroy, break
They destroyed the house
6 Knowingly.
Unknowingly
I made a mistake unknowingly.