Although carbon and hydrogen are better reducing agents,they are not used to reduce metallic oxides at high temperatures. Why?

Which oxide formation according to the Ellingham diagram shows a graph with a sudden change in slope?

The metal extracted by the electrolysis of its fused salt is

Limestone is present in the blast furnace production of iron in order to
$(I)$ provide a source of $CaO$
$(II)$ remove some impurities
$(III)$ supply $CO_2$

The incorrect statement about the Hall$-$Heroult process is:

Which of the following statements is not correct?
$1$. Reduction of alumina to give aluminium by magnesium is thermodynamically feasible.
$2$. The point of intersection of $Al_2O_3$ and $MgO$ curves in Ellingham diagram is below $1665 \ K$.
$3$. Use of magnesium as reducing agent in metallurgy of aluminium is economical.
$4$. Ellingham diagram represents the graphical plot of Gibbs energy vs temperature for the formation of the oxides of common metals and reducing agents.