1. Design an encoder for four input signals if one and only one is active at any moment in time.
2. Design an encoder for four input signals that outputs a zero code unless one and only one input line is active.
3. Obtain a single-bit full adder using
(a) a 3-to-8 line decoder and NAND gates, and
(b) 1-of-4 multiplexers,
(c) only NOR gates.