What is common about these molecules? a. their atoms are held together by covalent bonds. b. they are all made up of the same two atoms. c. their atoms are held together by ionic bonds. d. they are all made up of oxygen atoms only.

The answer is true for your question.

Ibelieve its because the stove is a cleaner burning fuel

Pretty sure it's d. heterogeneous is separated by physical properties. 

The question is incomplete. complete question is attached belowanswer: correct answer is option b  i.e.  solid particles  reason: filter paper has small pores, through which smaller particles can pass through. however, solid particles  have relatively larger size. hence, they are least likely to pass through.