Where is the os stored on a smartphone? a. read/write flash b. microprocessor c. rom d. ram?

The OS (Operating System) is stored in the ROM on a smartphone. Correct C

ROM stands for Read Only Memory. It is a computer memory that does not require power to store it's data (non-volitile).  It's the Internal Memory where the OS is stored. It is partitioned into two parts, one for the OS and the rest for apps to use.