A triangle has two sides that measure 0.5 meters and 1.5 meters. which could be the measure of the third side?

The third side of a triangle x, should be more than the difference between given two sides, and less than the sum.

x > (1.5 - 0.5)

x > 1

Also:

x < (1.5 + 0.5)

x < 2

1 < x < 2

x could be 1.1m, 1.2m, 1.3m, 1.4m, 1.5m, 1.6m, 1.7m, 1.8m, 1.9m.

It could be any of them.