
According to Archemedes Principle, weight of the body is balanced by the upward thrust force due to buoyancy.
At 0∘C, mg=A(100−20)ρ0∘Cg, where A is area of cross-section of cylinder and ρ0∘C is density of water at 0∘C.
At 4∘C, mg=A(100−21)ρ4∘Cg, where ρ4∘C is density of water at 4∘C.
ρ0∘Cρ4∘C=7980=1.01