Solution:

(i) As per the question,

$X=\{1,2,3\}$ in which $n$ represents any member of $X$

$X=\{1,2,3\}$

(ii) As per the question,

$X=\{1,2,3\}$ in which $n$ represents any member of $X$

$\begin{array}{l}
X=\{1,2,3\} \\
\{n-1 \mid n \in x\} \\
=\{1-1,2-1,3-1\} \\
=\{0,1,2\}
\end{array}$