The volume of water in the original water tank =5×4×2.5=50dm3.

The volume of iron = 4× 2 = 8 m3

The volume of water after adding iron blocks =50+8=58dm3.

Water depth =58 degrees (5×4)= 2.9 decimeters.

Distance from water tank mouth =3-2.9=0. 1dm.

∫2.9 decimeter < 3 decimeter

No water will overflow. There is still 0. 1 decimeter from the water tank mouth.