Which of the following is a SEQUENTIAL circuit ?

A sequential circuit is defined by its ability to store information, meaning its output depends not only on current inputs but also on the circuit's previous state. This requires memory elements like flip-flops or latches.\nA REGISTER is a collection of flip-flops used to store binary data. Because it retains its state until updated by a clock signal, it is the only sequential circuit among the options.\nIn contrast, PARITY circuits, ADDERS, and MULTIPLEXERS are combinational logic circuits. Their outputs depend solely on the present combination of inputs without any memory or feedback loops. For instance, an ADDER calculates a sum based on current bits only, while a REGISTER holds data over time. Therefore, the presence of memory elements makes the Register the correct sequential circuit.