Step-by-step Solution:

Full Adder – Sum Calculation
The sum output of a full adder with inputs $A$, $B$, and $C$ (carry-in) is calculated using the XOR (exclusive OR) operation.
$$ \text{Sum} = A \oplus B \oplus C $$ Where:
$A, B$ are the primary inputs
$C$ is the carry-in
$\oplus$ denotes the XOR operation
Correct Option: (c)