Option 1: aghast -> means shocked or horrified; too extreme for being puzzled by questions.
Option 2: horrified -> means filled with horror; doesn't capture the sense of being puzzled or unable to answer.
Option 3: baffled -> means confused or puzzled; perfectly captures being unable to answer or understand something.
Option 4: irritated -> means annoyed; relates to frustration rather than confusion or inability to answer.
Hence, Option 3: baffled -> "Stumped" means to be puzzled or unable to find an answer, which is exactly what "baffled" conveys when John struggles to answer his young son's curious questions -> correct