Answer
Very electropositive metals (i.e., very strong reducing agents) can only be isolated from their compounds by electrolysis. No chemical reducing agent is strong enough.
In the given list, $CaCl_{2}, NaCl$ and $Al_{2}O_{3}$ would require electrolysis.
Work Step by Step
Very electropositive metals (i.e., very strong reducing agents) can only be isolated from their compounds by electrolysis. No chemical reducing agent is strong enough.
In the given list, $CaCl_{2}, NaCl$ and $Al_{2}O_{3}$ would require electrolysis.