Is this the 150 or the 250 that can go under a concrete slab.

You want the 250 for under a concrete slab.

Can I use STYROFOAM™ Brand Extruded Polystyrene Foam Insulation under a basement floor? Yes. You can use STYROFOAM™ Brand Extruded Polystyrene Foam Insulation either around the perimeter of the basement floor or under the entire floor. In the U.S., Dow recommends using an ASTM C578, Type IV foam for residential basement floors, such as STYROFOAM™ Brand Square Edge Insulation or STYROFOAM™ Brand Tongue and Groove Insulation (both have 25 psi vertical compressive strength for weight support).