A Database contains one or more Rollback Segments to temporarily store "undo" information.
Rollback Segments are used :
To generate read consistent database information during database recovery to rollback uncommitted transactions for users
Schema objects are the logical structures that directly refer to the databases data. Schema objects include tables, views, sequences, synonyms, indexes, clusters, database triggers, procedures, functions packages and database links.
ORACLE database's data is stored in data blocks. One data block corresponds to a specific number of bytes of physical database space on disk
Oracle database consists of logical storage place which is called as blocks and the bytes in a block is set through DB_BLOCK parameter in parameter file
Yes objects of the same Schema reside in different tablespaces