As the vast majority of pipe organs are custom designed there is no one, definitive answer. A small, hand pumped, table top organ ("or Portative") might have as few as 25 pipes - or two octaves. The...
Ranks. Each "rank" has a unique name assigned to it.
Rene Magritte meant that it is an image of a pipe .
by gradually heating it
It depends on the number of ranks. Typically, there are 61 pipes per rank for keyboard ranks and 32 pipes per rank for pedal ranks.