This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Biochemistry
Which of the following is true about HPLC and gas chromatography? 
Select and explain. 
A. In Gas Chromatography, the stationary phase is always solid, B. In HPLC, the stationary phase is solid, C. In HPLC, the mobile phase is a liquid or solid, D. In Gas chromatography, the mobile phase is always gas
D: In Gas chromatography, the mobile phase is always gas
Answer: D: In Gas chromatography, the mobile phase is always gas 
Explanation: Ans. is 'd' i.e., In gas chromatography, the mobile phase is always gasif a solute has an affinity for the mobile phase, it moves faster. If a solute has an affinity for stationary phase, it gets retarded.That way, the solutes get separated based on differential distribution of them between a mobile phase and a stationary phase.