In simple words, data are contained inside blocks as well as an arbitrary integer that is necessary for producing the proof-of-work. In bitcoin blockchain, the block contains a header and relevant transaction data. A merkle tree of transactions is created and the hash of the root is included in the header. A merkle tree is a full binary tree of a hash values. At the bottom level of the tree, each transaction has a node containing its hash value. After that, the tree is constructed in a way such that the parent node has a value of the hash of the data contained in its children concatenating together.
The blockchain is designed in a way such that the average time for a block to be generated remains fairly constant. In the bitcoin blockchain, the average time for a block to generate is 10 minutes. Other blockchains may have a different time, e.g. 30 seconds, 5 minutes, etc.
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