3 physics questions !

1. Light-coloured surface reduces heat loss of the hot air inside the balloon by radiation. This is to prevent rapid cooling of the hot air which would make the balloon to descent and hence long distance travel cannot be accomplished.
2. convection.
The tea surrounding the ice cubes (which floats on the tea surface) gets cool and has higher density. The cooled tea thus sinks to the bottom and sets up a convection current.
3. This is to reflect the thermal radiation coming from the sun. A shiny colour surface reduces heat absorption by radiation. As a result, an optium temperature of the space telescope could be maintained more easily.