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

The IUPAC name of the compound
CH₃CH$$=$$CHC$$ \equiv $$CH is

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

How many bridging oxygen atoms are present in P₄O₁₀?