This type of hand drier contains a proximity sensor.  If you look underneath the drier, near where the air outlet is, you can see a small glass section, almost like a mini window pane.  If you were able to open this up and look inside, you would see an emitter which usually sends out an infra red pulse.  Next to the emitter is an infra red receiver.  The infra red source is too weak to bounce back from the floor to the receiver, but when you put your hand in the way the infra red beam bounces off your hands back into the receiver and it turns the hot air on.  Others are designed with just a receiver to pick up the infra red radiation emitted by your hands.

This is because antibiotics work in a very different way to bleach.  Bleach will kill pretty much everything, but antibiotics work in a much more subtle way.  Most antibiotics work by targeting specific proteins, such as ones in the cell wall, or those that help make other proteins.  A population of bacteria will have variation in genes between one bug and the next and so some will survive.  The bacteria that do survive are the ones with variations in their genes which let them cope against the drugs, and so these go on to divide and replace the ones killed by the antibiotics.  Bleach is so utterly destructive that virtually nothing survives, so no 'resistance' genes get spread throughout the population.

Most of the drugs we have are derived from a natural source, so bacteria have been locked in this 'arms race' for a very long time.  Long before we started using these chemicals to fight off infection.

This may be true, despite that fact that most people think of a virus as being something that makes them feel awful!  A recent piece of research in Nature by Skip Virgin, suggested that being infected by one of the family of viruses known as Herpes viruses, such as herpes simplex, which causes cold sores, Epstein-Barr virus, which causes glandular fever.  When they infected mice with the rodent equivalent of those infections, the mice developed a much better immune system than mice which had ever been infected.  To prove this, they exposed the mice to the bacteria which causes plague and also listeria, and they found these mice to be 100% protected against these bacteria compared with animals which had never been infected with a Herpes virus.  When they studies these mice they found molecules called interferon gamma at a much higher level, and this molecule is known to stimulate the immune system.  
They think that because we've been living with herpes viruses for millions of years, the body has come to rely on infection to provide additional gene function which our body no longer has.  This stimulated the immune system and we get some benefit.  It's almost a symbiosis, we give the virus a home and it gives us a better immune system.

The Aurora Borealis occurs because the Earth has a magnetic field.  The Sun is pumping out a million mile per hour maelstrom of charged particles and ions called the cosmic wind, and when this hits our magnetic field the two interact.  This is because charged particles are deflected by a magnetic field.  When this happens energy is released and this stimulates molecules in the atmosphere to get excited.  The dominant molecules in our atmosphere are oxygen and nitrogen, and when excited, oxygen emits light which is mainly green. Sometimes, particles in the solar wind have much higher energy than average, and these can make the oxygen more excited, and you get other colours.  
In terms of why you only see it on certain nights, it depends to some extent on how much solar activity there is, on atmospheric conditions and whether or not it's cloudy!  It only appears at the poles because the magnetic field lines are most concentrated near the north and south pole.

Yes they do.  If we take, for example, vitamin C, which is actually ascorbic acid, which in theory shouldn't be broken down in an acid environment.  We do rely on absorbing vitamins to remain healthy, so the body must have evolved mechanisms to absorb these without them being broken down.

Fire is the burning products of vapours of a fuel.  Whenever something burns it is first made into a vapour and mixed with oxygen, so when you have a fuel, such as paraffin or diesel, it works much better if it goes up a wick. This is because the heat can make vapour come from the wick to mix with oxygen in the air to cause a chemical reaction between the hydrocarbons in the fuel and the oxygen.  When this happens, you get complete combustion.  The flame that you see if just the hot gasses and soot particles, which are so hot that they glow.  Gas burns blue because it burns clean, and so there are very few soot particles in the flame to glow yellow.