Final answer:
A comma should be added after 'On Wednesday' in the sentence given, resulting in: 'On Wednesday, we can go to the mall.' The correct answer is option B.
Step-by-step explanation:
The appropriate punctuation mark to be added to the sentence “On Wednesday we can go to the mall.” is a comma. According to the rules of punctuation, when a sentence includes a day of the week that is directly followed by another clause, a comma should be placed after the day of the week to separate it from the rest of the sentence.
Hence, the sentence should read: “On Wednesday, we can go to the mall.” This follows the guidelines that commas are used to set off the days of the week when these are followed by additional information.