Which of the following fuels has the highest calorific value?

Which alloy is used for making statues and medals?

Give reasons for the following:
$(i)$ Alloys are used in electrical heating devices rather than pure metals.
$(ii)$ Gold ornaments look new even after several years of use.
$(iii)$ An iron grill should be painted frequently.

Account for the following:
$(a)$ Aluminium is more reactive than iron,but its corrosion is less than iron.
$(b)$ Hydrogen gas is not evolved when zinc metal reacts with dilute $HNO_3$.
$(c)$ Carbon is not used for reducing aluminium from aluminium oxide.

In a blast furnace,what prevents the oxidation of molten iron?

What is thermit reaction? How is it used to join the railway tracks or cracked machine parts?