Computational Circuit:
A computational circuit is a collection of logic gates that perform a specific computational task. It takes a set of inputs, performs logical operations on them, and produces an output based on the results of these operations. Computational circuits are used in various applications, including digital computers, calculators, and other electronic devices.

Logic Circuit:
A logic circuit is a type of computational circuit that consists of logic gates. Logic gates are electronic devices that perform logical operations on one or more binary inputs and produce a binary output. They are the building blocks of digital circuits and are used to implement Boolean functions.

Design Circuits:
Design circuits refer to the process of designing computational or logic circuits. It involves selecting appropriate logic gates, arranging them in a specific configuration, and connecting them to form the desired circuit. Designing circuits requires a thorough understanding of logic gates and their behavior.

Register:
A register is a digital circuit element used to store data. It consists of a group of flip-flops, which are basic memory units capable of storing one bit of data. Registers are used in computer systems for various purposes, such as storing instructions, data, or the results of computations.

Explanation:
Among the given options, the correct answer is option 'A' - Computational Circuit. A set of input and output arrangement refers to a computational circuit, which is a collection of logic gates that perform a specific computational task. These circuits take a set of inputs, process them using logic gates, and generate an output based on the results of these operations.

Logic circuits, on the other hand, are a type of computational circuit that specifically consists of logic gates. They are used to implement Boolean functions and are the building blocks of digital circuits.

Design circuits refer to the process of designing computational or logic circuits. It involves selecting appropriate logic gates, arranging them in a specific configuration, and connecting them to form the desired circuit.

Registers, on the other hand, are digital circuit elements used to store data. They are not directly related to the arrangement of logic gates for input and output.

Therefore, the correct answer is option 'A' - Computational Circuit.