The compound 'B' gives a red color with FeCl₃, which is a characteristic test for phenols. This indicates 'B' is a phenolic compound. The reaction involves the formation of a colored complex between the phenolic group and the ferric ion. Among the options, only the structure with a free phenolic -OH group will give a positive test. The correct structure is the one where the -OH is not methylated and is available for complex formation.

Final Answer: $B={C{H}_{3}O}_{}-{C6H_4-OH}_{}$