Series to Parallel Converter:
A series to parallel converter is a circuit that takes a series input and converts it into a parallel output. This type of converter is commonly used in various applications where the input needs to be distributed to multiple outputs.

Options:
a) Encoder: An encoder is a circuit that converts multiple inputs into a coded output. It is used in applications such as data compression, error detection, and data transmission. It does not perform the function of converting a series input into a parallel output, so it cannot be used as a series to parallel converter.

b) Decoder: A decoder is a circuit that performs the reverse operation of an encoder. It takes a coded input and converts it into multiple outputs. Like an encoder, it does not convert a series input into a parallel output, so it cannot be used as a series to parallel converter.

c) De-multiplexer: A de-multiplexer, also known as a demux, is a circuit that takes a single input and directs it to one of several outputs based on control signals. It has multiple outputs, making it suitable for converting a series input into a parallel output. Therefore, a de-multiplexer can be used as a series to parallel converter.

d) Multiplexer: A multiplexer, also known as a mux, is a circuit that combines multiple inputs into a single output based on control signals. It does not convert a series input into a parallel output, so it cannot be used as a series to parallel converter.

Conclusion:
The correct option is c) De-multiplexer, as it can be used as a series to parallel converter by directing a series input to multiple parallel outputs based on control signals.