Question 4
Which of these is a homogeneous mixture?
The right answer is the one marked above.
A salt solution. It is a mixture — the salt and the water are merely mingled, not chemically joined — and it is the same throughout, which is what homogeneous means.
Sand and water is a mixture too, but a heterogeneous one: it is plainly not the same throughout. Carbon dioxide is a compound and copper an element — both pure substances, not mixtures at all.