You must learn the terminology to follow along in chemistry. If in doubt Google the term...
Eluent - As Zhe noted "Eluent is a fancy name for solvent in chromatography." It can be a gas or a liquid. For TLC or HPLC a liquid is used. For GC a gas is used.
Normal phase TLC - For normal phase TLC the stationary phase is polar and the mobile phase is typically non-polar or only moderately polar. Polar molecules are attracted to the stationary phase while non-polar compounds are carried along by the mobile phase.
Reverse phase TLC - For reverse phase TLC the stationary phase is non-polar and the mobile phase is typically moderately polar to strongly polar. Non-polar molecules are attracted to the stationary phase while polar compounds are carried along by the mobile phase.
The normal designations is because the first HPLC columns used alumina and silica packing, which are both polar, in columns. With setup The least polar compounds were eluted first and the most polar compounds were eluted last.
Switching to non-polar packing was then noted as reverse phase since it reversed the order of elution. The most polar compounds were eluted first and the least polar compounds were eluted last.
ANSWER
This is normal phase TLC so the stationary phase is polar.
Assuming the compounds are "relatively" polar
Plate 2 has the LEAST polar eluent because the compounds have lower $\text{R}_{\text{f}}$ values than they do on the other two plates.
Plate 3 has the MOST polar eluent because the compounds have higher $\text{R}_{\text{f}}$ values than they do on the other two plates.
On plate 3 the least polar compound would be Z.
Assuming the compounds are "relatively" non-polar
Plate 2 has the MOST polar eluent because the compounds have lower $\text{R}_{\text{f}}$ values than they do on the other two plates.
Plate 3 has the LEAST polar eluent because the compounds have higher $\text{R}_{\text{f}}$ values than they do on the other two plates.
On plate 3 the least polar compound would be Z.
So the problem would seem to be ambiguous. We don't know that any of the solvents is "absolutely" non-polar like hexane, or that one might be "absolutely" polar like water.