\documentclass[12pt,a4paper]{book}
\usepackage{amsmath,amssymb,amsthm,paralist}
\usepackage{xepersian}
\settextfont[Scale=1]{Yas}

\begin{document}

\begin{inparaenum}\setlength{\itemsep}{1cm}
\item[(ج)]$2i$ 
\item[(چ)]$2i$ 
\item[(ح)]$2i$ 
\end{inparaenum}

\end{document}