\textbf{169.} According to the figure below, a certain amount of ideal gas undergoes a process from state $i$ to state $f$. Which of the following statements about this process is correct?
\textit{[Figure: P-V diagram showing a curved path from point $i$ at $(V_1, P_1)$ to point $f$ at $(3V_1, 0.4P_1)$]}
\begin{enumerate}
\item The process is isothermal.
\item The process is adiabatic.
\item The gas has absorbed heat.
\item The work done on the gas is positive.
\end{enumerate}