Molecular is every element present in the compound eg C2H6, empirical is the smallest whole number ratio of elements in a compound so that would be CH3 as you divide by the highest common factor. Some compounds only have 1 formula if they are simple or have no common factors. Eg methane, CH4 is its molecular and empirical because its the simplest whole number ratio and includes every element in the molecule
Answer
Sounds travel slowest in gasses so it would be air
