Answer
$0$ element: $\{\}.$
$1$ element: $\{a\},\{b\},\{c\},\{d\}$
$2$ elements $\{a,b\},\{a,c\},\{a,d\},\{b,c\}, \{b,d\} ,\{c,d\}$
$3$ elements $\{a,b,c\},\{a,b,d\},\{a,c,d\},\{b,c,d\}$
$4$ elements $\{a,b,c,d\}$
Work Step by Step
The given set has $4$ elements so it has $2^4=16$ subsets.
These subsets are:
$0$ element: $\{\}.$
$1$ element: $\{a\},\{b\},\{c\},\{d\}$
$2$ elements $\{a,b\},\{a,c\},\{a,d\},\{b,c\}, \{b,d\} ,\{c,d\}$
$3$ elements $\{a,b,c\},\{a,b,d\},\{a,c,d\},\{b,c,d\}$
$4$ elements $\{a,b,c,d\}$
