Why is in used 'in' the sentence "in the corner of the room" and why is is 'at' used in the sentence" at the corner of the road"?

Dear student,

The preposition “in” implies 'being within something, inside the edges of something'. 'In teh corner of the room' means withing the clear defined edges of the corner of the room.
'At' is used to talk about specific points in space: at the corner of the road. (You cannot be confined within the corner of the road.)

Regards