Acidified K₂Cr₂O₇ solution turns green when Na₂SO₃ is added to it. This is due to the formation of

For the four successive transition elements (Cr, Mn, Fe and Co), the stability of + 2 oxidation state will be there in which of the following order?
(At. nos. Cr = 24, Mn = 25, Fe = 26, Co = 27)

Which of the following oxidation states is the most common among the lanthanoids?

Match List I (substances) with List II (processes) employed in the manufacture of the substances and select the correct option.

Column $${\rm I}$$ (Substances)			Column $${\rm I}$$$${\rm I}$$ (Processes)
(A)	Sulphuric acid		(i)	Haber's process
(B)	Steel		(ii)	Bessemer's process
(C)	Sodium hydroxide		(iii)	Leblanc process
(D)	Ammonia		(iv)	Contact process