Hi Space-wise - You can use IN when something is located inside of a particular space (for example "in the boxe a box, in the house, or in the car, water is in the glass). ON - when something is touching the surface of something, such as " on the desk, on the chair, on the road, on the pavement). Time-wise: "IN" - use it when talking about months ( in January), years ( in 1990), centuries ( in 21st century) but also longer periods ( in the summer) "ON" - use it to talk about DAYS ( on Monday...) and DATES ( Xmas is on 25th December...) Hope this helps.

Hi Space-wise - You can use IN when something is located inside of a particular space (for example "in the boxe a box, in the house, or in the car, water is in the glass). ON - when something is touching the surface of something, such as " on the desk, on the chair, on the road, on the pavement). Time-wise: "IN" - use it when talking about months ( in January), years ( in 1990), centuries ( in 21st century) but also longer periods ( in the summer) "ON" - use it to talk about DAYS ( on Monday...) and DATES ( Xmas is on 25th December...) Hope this helps.