Why even in after load and store operation RACK signal is given as an acknowledgement? why not WACK in case of store operations?
RACK and WACK correspond to transactions completing on the AR and AW channels respectively. AR requests require the ACE manager to give a RACK, and AW requests require the ACE manager to give a WACK.
For ACE managers, coherent stores are typically* performed by the ACE manager obtaining a Unique copy of the cache line within its cache. This is generally performed using an operation on the AR channel, and so a RACK response is given.
* The exceptions here are Write[Line]Uniques and memory update operations which are issued on the AW channel and so would result in a WACK response being given.