Introduction:
A BCD (Binary Coded Decimal) to Seven Segment Decoder is a device that takes a binary input in BCD format and converts it into a seven-segment display output. The seven-segment display is a commonly used electronic display device that can display decimal numbers and a few alphabets using seven individually controlled segments. Each segment corresponds to a particular input combination, and the decoder maps the BCD input to the appropriate combination to light up the corresponding segments.

Explanation:
The correct answer for the device that converts BCD to Seven Segments is option 'B' - Decoder.

Decoders:
A decoder is a combinational logic circuit that converts coded inputs into coded outputs. It has multiple input lines and multiple output lines, and each input combination produces a unique output combination. Decoders are widely used in digital systems for various applications, such as data decoding, address decoding, and display decoding.

BCD to Seven Segment Decoder:
A BCD to Seven Segment Decoder is a specific type of decoder that takes a four-bit BCD input and converts it into a seven-segment display output. The BCD input is typically represented by four binary bits, each corresponding to a decimal digit (0-9). The seven-segment display consists of seven individual LED segments (a-g) that can be lit up in different combinations to display the decimal digits.

Working:
The BCD to Seven Segment Decoder has four input lines for BCD input (D0-D3) and seven output lines for the seven-segment display (a-g). Each output line corresponds to a particular segment of the seven-segment display. By analyzing the BCD input combination, the decoder activates the appropriate output lines to light up the corresponding segments and display the desired decimal digit.

Example:
For example, if the BCD input is '0100', which represents the decimal digit '4', the decoder will activate the appropriate output lines to light up the segments 'a', 'b', 'e', and 'f'. This will result in the seven-segment display showing the digit '4'.

Conclusion:
In conclusion, a BCD to Seven Segment Decoder is the correct device for converting BCD input into a seven-segment display output. It analyzes the BCD input combination and activates the appropriate segments of the seven-segment display to display the corresponding decimal digit.