Are all instructions eventually converted to zero-operand instructions? Recently, my demonstrator said that all instructions are eventually converted to zero-operand instructions just before they get executed. yet another demonstrator said that this "doesn't make any sense", and I don't know who to believe; none of them really gave any logical arguments.

So, I want to know is any of them right at all? I tried searching for the answer but I didn't find anything.
This will depend on the computer architecture.  zero-operand computer architectures use the stack, so to add 2+2:


PUSH 2 (into the stack),    
PUSH 2 (again),  
ADD (call the instruction - note that no operators are passed by).
POP ( 4 out of the stack)


but most other computer architectures e.g. use registers, memory addresses and values as the parameters to an instruction (in addition to the stack). For example the same 2+2 in a CISC computer.


MOX AX,02 (AX=0)
ADD AX,02 (AX=4)


However, if you're thinking in terms of translating a high level programming language into executable code e.g. one routine calling a subroutine the list of parameters most likely be passed by via stack and the number of parameters be reduced to 0 as in the first example.