How many maximum output lines would be there in a 4-input decoder? Draw the logic gate diagram for…

A decoder with $n$ inputs has a maximum of $2^n$ output lines. For a 4-input decoder, maximum output lines $= 2^4 = 16$.

Application of an encoder: used in keyboard encoders — to convert the key pressed by the user (a decimal/alphanumeric character) into its equivalent binary (e.g. ASCII) code for the computer to process. (Other valid answers: priority encoders in interrupt-handling systems, decimal-to-BCD encoders in calculators.)