Answer: B.two gases
Explanation: Homogeneous mixtures are mixtures in which dispersed phase is uniformly distributed throughout the dispersion medium and there is no physical boundary between the dispersed phase and dispersion medium.
Heterogeneous mixtures are mixtures in which dispersed phase is not uniformly distributed throughout the dispersion medium and there is a distinct physical boundary between the dispersed phase and dispersion medium.
a) Two liquids may or may not be completely miscible thus may form a homogeneous (milk and water) or a heterogeneous mixture (oil and water).
b) Two gases always form a homogeneous mixture as there is large vacant spaces present between the molecules.
c) A solid and a liquid may or may not be completely miscible thus may form a homogeneous (salt and water) or a heterogeneous mixture ( sand and water).
d) A liquid and a gas may or may not be completely miscible thus may form a homogeneous (river water) or a heterogeneous mixture (perfume spray).