Explanation:

The 'compare' operation, which involves evaluating conditions such as greater than, less than, or equality between values, is a 'Logical function of ALU' (Arithmetic Logic Unit). Option (b) correctly identifies this. 'Arithmetic function of ALU' (a) involves mathematical calculations like addition or subtraction. The ALU does not handle 'Input and output of ALU' (c) directly in the sense of data transfer to/from peripherals. Therefore, comparing falls under the logical capabilities of the ALU.