Final answer:
The error in the sentence is related to punctuation; a question mark is incorrectly used. Additionally, there is a factual inaccuracy as 'March 41' is not a valid date.
Step-by-step explanation:
The error in the sentence "Mother's Day is on March 41?" is related to punctuation, specifically the use of a question mark. Mother's Day is a known date and stating it does not require a question mark. Additionally, April (not March) has a day numbered '41' since the month of March only has 31 days. However, '41' is not a valid date in any month, so there's a factual error, but that is not an option provided in the selections.