Let's analyze the given data to determine which group's data is obviously unreliable.
We have the results in a table format:
[tex]\[
\begin{tabular}{|c|c|c|}
\hline
Group & Vegetable oil removed (mL) & Engine oil removed (mL) \\
\hline
1 & 10 & \\
\hline
2 & 110 & 20 \\
\hline
3 & 60 & 130 \\
\hline
4 & 80 & 40 \\
\hline
\end{tabular}
\][/tex]
We notice that Group 1's data is missing the amount of engine oil removed. This makes their data incomplete and therefore unreliable when compared to the data from the other groups, which all provided both vegetable oil and engine oil removal amounts.
Thus, the group whose data is obviously unreliable is:
Group 1