The fundamental motivation for decomposition is to remove harmful redundancy and the anomalies caused by that redundancy.
Therefore, D is correct.
Now consider the other options.
A is not guaranteed.
Although decomposition often reduces duplicated information, separate relations also repeat linking/key attributes.
Physical storage depends on the actual data and representation, so storage cannot be guaranteed to decrease for every instance.
B is incorrect.
Decomposition does not eliminate relational operations such as joins or Cartesian products.
In fact, decomposed relations often have to be joined to answer queries.
C is incorrect.
Some queries may become more expensive after decomposition because information that was previously in one table may now require a join.
Therefore, the reliable design benefit here is elimination of update anomalies caused by redundancy.
Hence, the correct answer is D.
