Yes, the liquid can flow.
1.Unlike solids, fluids (liquids and air) have the property called viscosity which is defined as the magnitude of internal friction in a fluid.
2.The causes of viscosity are due to two factors: (i) cohesive forces; (ii) momentum diffusion.
3. Not all the liquids flow easily. Liquids with high viscosity, such as honey and mayonnaise, are relatively difficult to flow.
No, we can't keep a particular gas in an open container.in an open container, the pressure becomes equal to atmospheric pressure and due to molecular dispersion, purity of that particular gas reduced.
Actually, a gas inside a closed container doesn't necessarily experience atmospheric pressure. If you've ever shaken a bottle of pop then opened it you'll know that the gas pressure inside is a lot higher than atmospheric pressure. This is an example where the pressure inside the closed container is higher than atmospheric pressure, but it can be lower as well.