Question

Which condition is necessary for a mold fossil to form

Answer 1

If someone can just say the number, those who understood the previous guy, just interpret what they said in direct answer form for the dumb, like me :)

Answer 2

First, the organism needs to be buried quickly so the bones do not rot, sinking in tar, sand storm sinking in mud etc. Over time more sediment will cover the organism, preventing decay. Being buried quickly and preserved away from predators are one of the reasons why marine life fossils are much more common the terrestrial animals as they are rarely preserved.