Final answer:
The most common unit for the x-axis on a calibration curve is molarity (mol/L), due to its widespread use in laboratory settings for consistency and ease of stoichiometric calculations.
Step-by-step explanation:
The appropriate units for the Concentration (x-axis) on a calibration curve would typically be molarity(mol/L). Molarity is a common unit for expressing concentrations of solutions in chemistry, especially when dealing with reactions that occur in aqueous solution or when referencing standard concentrations. However, depending on the context of the experiment and the range of concentrations, other units might be used such as mass percent, volume percent, parts per million (ppm), or parts per billion (ppb).
When creating a calibration curve, it's important to use the same units of concentration throughout the experiment to ensure consistency and accuracy in the results. In most laboratory settings, molarity is favored because it directly relates the number of moles of solute to the volume of solution, thus facilitating stoichiometric calculations and comparisons.