Which one of the following lanthanoids does not form $MO_{2}$? [$M$ is lanthanoid metal]

Which of the following elements have half-filled $f$-orbitals in their ground state?
(Given: atomic number $Sm = 62$; $Eu = 63$; $Tb = 65$; $Gd = 64$; $Pm = 61$)
$A.$ $Sm$ $B.$ $Eu$ $C.$ $Tb$ $D.$ $Gd$ $E.$ $Pm$
Choose the correct answer from the options given below:

Which one of the following elements shows the maximum number of different oxidation states in its compounds?

Choose the correct option regarding the following.
Assertion: Actinides exhibit a larger number of oxidation states than lanthanides.
Reason: There is a large energy gap between $5f$,$6d$ and $7s$ sub-shells.

Which of the following ions is the strongest oxidizing agent? [ Atomic Number of $Ce = 58, Eu = 63, Tb = 65, Lu = 71$ ]

What is the general formula of lanthanoid hydroxide? (Consider $Ln$ as any lanthanoid element)