Liquid phase exists for all compositions above the isometric region.

Explanation:
The liquid phase exists in the phase diagram of a substance at temperatures and pressures where the substance is in a liquid state. The phase diagram is a graphical representation of the various phases (solid, liquid, and gas) that a substance can exist in, at different temperatures and pressures.

The isometric region, also known as the liquid region, is the region in the phase diagram where the substance exists as a liquid. This region is bounded by the melting point curve and the vaporization curve.

- Liquid phase above the eutectic region:
The eutectic region is a specific composition in the phase diagram where a eutectic mixture forms. In this region, the substance undergoes eutectic solidification, which means that it solidifies as a mixture of two or more components. Above the eutectic region, the substance exists in the liquid phase, as it has not reached the composition required for eutectic solidification.

- Liquid phase above the equilibrium region:
The equilibrium region is the region in the phase diagram where the substance exists in equilibrium between the solid and liquid phases. In this region, the substance can exist as a mixture of solid and liquid, depending on the temperature and pressure. Above the equilibrium region, the substance exists in the liquid phase, as it has not reached the conditions for equilibrium between the solid and liquid phases.

- Liquid phase above the sublimation region:
The sublimation region is the region in the phase diagram where the substance undergoes sublimation, which means it directly converts from a solid to a gas phase without passing through the liquid phase. Therefore, the liquid phase does not exist above the sublimation region.

Hence, the correct answer is option C, the liquid phase exists for all compositions above the isometric region.