How many nodes need to validate a newly created block? It must be impossible for a newly created block to be propagated and validated by every node in bitcoin network considering offline nodes and the ones with poor Internet connectivity. 

How many validations is sufficient for a newly create block to be added as the latest block?
Every node in the Bitcoin network acts independently. When a node hears about a new block, it will perform a series of checks to see if it is valid according to the network's rules. 

If the block is valid, the node adds it onto it's local copy of the blockchain, and broadcasts the block to the other nodes its connected to.

If the block isn't valid, the node will reject it, and not broadcast it. 

So by following the network's rules, even though each node acts independently, together the network is able to remain in consensus regarding the blockchain history.