The lanthanide contraction relates to

$Ce$ $(Z=58)$ is a member of

What are the products formed when lanthanoids $(Ln)$ react with $1$. $H_2O$ and $2$. $N_2$?

Fill in the blanks given below:
$(i)$ Neptunium and Plutonium are obtained from ............ .
$(ii)$ Lanthanoid series and Actinoid series are known as ............ .
$(iii)$ The main energy level of an atom is called ............ .
$(iv)$ Elements that possess both metallic and non-metallic properties are called ............ .

$A$ lanthanoid has $n$ unpaired electrons and another lanthanoid has $(14-n)$ unpaired electrons. It means:

Identify the correct statements about lanthanoids:
$I$. $Ce^{4+}$ and $Tb^{4+}$ act as oxidising agents.
$II$. $Eu^{2+}$ and $Yb^{2+}$ act as reducing agents.
$III$. Mischmetal is an alloy of $95 \%$ lanthanoid metal and $5 \%$ iron.
$IV$. $La^{3+}$ and $Ce^{4+}$ are diamagnetic in nature.