Relative volatility varies with the concentration of component for an ideal solution. The relative volatity of a binary mixture may be defined as the ratio of vapor pressure of component 'A' to that of component 'B', when

• A. only vapor phase follows Raoult's law.
• B. only liquid phase obeys Dalton's law.
• C. liquid phase obeys Dalton's law and vapor phase obeys Raoult's law.
• D. Vapor phase obeys Dalton's law and liquid phase obeys Raoult's law.