NTSE Stage 2 SAT 2014 Question Paper

Metals like sodium, potassium, calcium and magnesium are extracted by electrolysis of their chlorides in molten state. These metals are not extracted by reducing of their oxides with carbon because
(a) reduction with carbon is very expensive
(b) carbon readily makes alloy with these metals
(c) carbon has less affinity for oxygen than these metals
(d) carbon is weaker reducing agent than these metals