The total volume of the cube is:
\[V_{{total}} = (10 { cm})^3 = 1000 { cm}^3\]
The mass of the cube is:
\[m = 400 { g} = 0.4 { kg}\]
The density of the cube is:
\[\rho_{{cube}} = \frac{m}{V_{{total}}} = \frac{0.4}{1000 \times 10^{-6}} = 400 { kg/m}^3\]
As the cube floats, the submerged volume is calculated as:
\[V_{{submerged}} = V_{{total}} \times \frac{\rho_{{cube}}}{\rho_{{water}}}\]
\[V_{{submerged}} = 1000 \times \frac{400}{1000} = 600 { cm}^3\]
Consequently, the volume of the cube that is not submerged in water is:
\[V_{{outside}} = V_{{total}} - V_{{submerged}}\]
\[V_{{outside}} = 1000 - 600 = 400 { cm}^3\]
Therefore, the correct answer is (4) 400 cm³.