The correct option is B 300 cm3
The weight of the cube is balanced by the buoyant force. The buoyant force is equal to the weight of the water displaced. If V volume of the cube is inside the water, the weight of the displaced water =Vρ g, where ρ is the density of water. Thus,
Vρg=700×g
⇒V=700ρ=700 cm3
The total volume of the cube =(10 cm)3=1000 cm3.
∴ The volume of cube outside the water is 1000 cm3−700 cm3=300 cm3