hi
I would like to know Which 16 channel Multiplexer / Demultiplexer IC should i use
for the CKT. in attachment.
or any other alternative for this CKT.

 

The upper 16 to 4 device is a priority encoder, however I don't know of any above the 74HC148 which is 8:3 in size, so some glue logic will be needed to splice 2 devices together.

The lower 4 to 16 device is any multiplexer, which in the CMOS CD4067 comes as a multiplexer/demultiplexer and you choose the direction. It leaves the unselected outputs floating so your circuit needs to accept that.