MWE,
\documentclass[a4paper,11pt]{article}
\usepackage[utf8]{inputenc}
\begin{document}
120 kHz ’e
\textit{120 kHz ’e}
\end{document}
and output,

Sometimes this red line is getting longer. Why not red line is short? I didn't find solution about this question. Does anyone know how to fix it? (My english text changeable)


\,(say). See What commands are there for horizontal spacing? – Werner Apr 15 '15 at 21:32