Concept- Homophones are the words that sound similar.
An aisle, given in option 1, is that the passage between long rows of seats in a very church, library, or theater. It also indicates such a passage in an aircraft or a train.
Isle in option 2 is additionally wrong. Isle is another word wont to represent a smaller island or a peninsula. As this cannot form a meaningful sentence ere, we rule out this feature.
Option 3 is that the right answer. I’ll is that the contracted type of I shall or i'll. ‘I will sit up for the passengers to board’ thus completes the sentence.
Option 4 is wrong as ale, in British context, refers to an alcoholic drink; particularly a variant of beer. it might be quite meaningless to use this word here and hence wrong.
Hence , the correct answer is option 3 - I’ll.