3CH4 and C3H12 have the same number and kind of elements. How are they different?

3CH4 refers to three molecules of a compound and C3H12 refers to only one molecule of a compound.
3CH4 and C3H12 are actually different molecules though they contain the same number and types of atoms. Recall that both of them are hydrocarbons hence they contain only hydrogen and carbon.
3CH4 refers to three molecules of methane while C3H12 refers to one molecule of diphenyl methane. Hence 3CH4 refers to three molecules of a compound and C3H12 refers to only one molecule of a compound.
Learn more: https://brainly.com/question/8646601