why water is in liquid state? and how does it know 100 degrees centigrade is the boiling point? and how does it know to convert at this temperature?

dear katroth 
good queation , water also have gas state thats water vapour and also solid state thats ice cube . 
so, its actually the intermolecular force of attraction thats plays a vital role here . 
the temp that you are talking about is required to break its intermolecular force of attraction bonds , and it interchanges its state . 
HOPE IT CLEARS 
kindly approve