Explanation:

The CPU (Central Processing Unit) is physically implemented as an integrated circuit, commonly referred to as a 'Chip' or microprocessor. Option (a) 'Chip' is the most appropriate term among the choices to describe the physical form of a CPU. Option (b) 'Box' refers to the computer's casing or chassis. Option (c) 'Circuit' is too general, as many components are circuits. Option (d) 'Peripheral' refers to external devices connected to the computer, not the CPU itself. Therefore, 'Chip' is the best fit.