The best option is a. but it is not complete!
Both liquids have different densities, it's true. But they are immiscible liquids and they don't form a solution.
Explanation:
NH4OH(aq) ---> NH4+(aq) + OH-(aq)
Gravity is a force that acts between the Earth's mass and the mass of other objects that surround it. ... Astronauts merely feel weightless because there is no external contact force pushing or pulling upon their body. They are in a state of free fall.