\documentclass[12pt,a4paper]{book}
\usepackage{graphicx,amsmath,amssymb,amsthm,amsfonts,paralist}
\usepackage{xepersian}

\begin{document}
\begin{itemize}
\item[1.]
\begin{inparaenum}
\item[(الف)]$2i$
\item[(ب)]$-i$ 
\item[(پ)]$\frac{1}{2}-\frac{1}{2}i$ 
\item[(ت)]$18+i$ 
\item[(ث)]$-\frac{1}{5}+\frac{3}{5}i$ 
\item[(ج)]$1+i$ 
\item[(چ)]$0$ 
\item[(ح)]$1+i$
\end{inparaenum}
\item[2.]
\end{itemize}
\end{document}