Explanation:

- Contiguous means being in contact or touching along a boundary or at a point.

- Option 1: Contactual - This option isn't directly related to the context of physical touch or proximity. Contractual typically deals with agreements or formal arrangements, not physical placement.

- Option 2: Separated - This is the opposite of contiguous because it implies a gap or distance between items. Items that are separated are not touching or connected.

- Option 3: Neighbouring - This term suggests closeness or adjacency, much like contiguous, and is thus not an antonym.

- Option 4: Adjoining - Similar to contiguous, adjoining means next to or in contact with.