Virtual memory is disk drive space that is manipulated to seem like RAM. Software creates virtual memory by swapping files between RAM and the disk drive. This memory management technique effectively creates more total memory for the system's applications to use. When the system runs out of available RAM, it shifts data to the virtual memory swap file on the disk drive. However, because there is a major transfer of information that involves the hard disk drive, an overall reduction in speed is encountered with virtual memory operations.

It depends on the compiler where it stores. Most of the times it is in RAM. The only thing that the standard says is that it will have the lifetime equal to that of process.

 RAM: Read / Write memory, High Speed, Volatile Memory. ROM: Read only memory, Low Speed, Non Voliate Memory.

Stack is a portion of RAM used for saving the content of Program Counter and general purpose registers.

No. ROM cannot be used as stack because it is not possible to write to ROM.

If your programs are accessing lots of memory in lots of places, many page faults will occur in order to read in the pages that were paged out. Because all of RAM  being used, for each page read in to be accessed, another page must be paged out. This can lead to more page faults, because now a different page of memory has been moved to disk.This problem of many page faults occurring in a short time, called page thrashing, can drastically cut the performance of a system.