Super! Tea normally consists of water/milk, tea particles and sugar. Atmospheric air is made up of many different gases like Nitrogen, Oxygen, etc. So, both these are mixtures. The gold chain is made only of gold. So, it cannot be a mixture.
Look at the two images here. In one, we have a cup of tea. In another, we have some iron and sand mixed together.

Matter is said to be homogeneous if it is uniform. That is, if you look at the particles in a homogeneous mixture, you cannot see the different particles separately.
Which of the two mixtures is homogeneous?
  • Tea
  • Iron and sand mixture
  • Both mixtures
  • Neither mixture