This one is correct (as I'm sure I0 knows).

From perldoc -f pack:

c   A signed char value.
...
i   A signed integer value.
    (This 'integer' is at least 32 bits wide.  Its exact
    size depends on what a local C compiler calls 'int',
    and may even be larger than the 'long' described in
    the next item.)

The question asks specifically for signed 8-bit, which is "c", a signed char value (8 bits). "At least 32 bits" is not 8 bits.