Final answer:
The truthfulness of the statement about the presence of a fluorine compound in a mixture, such as methyl fluoroacetate, cannot be determined without context. CH3 CH2COOH and C3H6O2 could be structural isomers, and calculating the number of fluorine atoms or the substance with the least number of molecules requires additional data and calculations.
Step-by-step explanation:
The statement 'A mixture contained no fluorine compound except methyl fluoroacetate' can either be true or false based on the context provided in other related questions. However, without additional context, we cannot determine its accuracy.
Regarding the question on structural isomers, two molecules with the formulas CH3 CH₂COOH and C3H6O2 could indeed be structural isomers because they have the same molecular formula but could have a different arrangement of atoms.
For the composition containing hydrogen, carbon, and fluorine, to calculate the number of fluorine atoms present in a compound from the given percentages by mass, we need the molar mass of the compound, which is not provided.
Finally, to identify the substance with the least number of molecules from given options, we would divide the mass of each sample by its respective molar mass to find the number of moles, and then use Avogadro's number to determine the number of molecules.