Which of the following observations would indicate that a material is a pure substance?
It does not dissolve in water.
It changes color after heating.
It cannot be physically broken down into different types of atoms.
It can be physically broken down into different types of molecules.
"cules

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.

The answer is  d.  hydrogen