Which is the interrupt vector that functions as invalid opcode?

The correct answer is C. 7.

The interrupt vector that functions as invalid opcode is 7. This means that if the CPU encounters an instruction that it does not recognize, it will generate an interrupt and transfer control to the interrupt service routine at address 00007h.

The other options are incorrect because they do not correspond to interrupt vectors that function as invalid opcode. Option A, 9, is the interrupt vector for the keyboard. Option B, 8, is the interrupt vector for the timer. Option D, 6, is the interrupt vector for the serial port.

I hope this helps!