Explain why solids have greater densities than liquids and liquids have greater densities than gases.

Does a body having a relative density of $1.2$ will sink or float in water and why?

Does a body having a relative density of $0.8$ will sink or float in water and why?

A test tube filled with a solid sinks (to a certain mark) in a container filled with milk. If water is added to the milk, will the test tube sink more or will it move up in the container?

Ankur goes to a jewellery shop and buys a gold locket. When he comes back home, he looks up the density of gold, which he finds to be $19.3 \mathrm{g}/{\mathrm{cm}}^3$. How can he determine if the locket he has bought is of pure gold?