The answer given on the textbook is figure 2. But How can the Needle be centered if the aircraft is not on the radial?
The aircraft is on a radial. Just not the one marked on the diagram.
Notice that figures 1, 3, and 4 all have heading 210° dialed at the top of the instrument. However, figure 2 has heading 120° selected. Since the needle is centered with a "TO" indication, this indicates that the plane is on the 300° radial (the reciprocal of 120°). In other words, the plane is northwest of the VOR, which matches with the diagram.
You can rule out 4 straight away - it is flagged as Off.
It is worth noting that the horizontal marker blips on a CDI represent 2 degrees when tracking a VOR (the first 2 degrees being the edge of the central circle).
So with that in mind number 1 indicates something like 5 degrees right of track, which would put you on the 215 radial from the VOR. The image clearly does not show an aircraft on the 215 radial.
A similar picture for 3 showing 8 degrees right of 215 radial to the VOR which would make the aircraft on about the 022 radial - again clearly not the case.
So that just leaves 2 which as the other answer correcty says matches the picture.