Invar,an alloy of $Fe$ and $Ni$,is used in watches and meter scales. Its characteristic property is:

Match List-$I$ with List-$II$

List-$I$ Species	List-$II$ Electronic distribution
$A$. $Cr^{2+}$	$I$. $3d^8$
$B$. $Mn^{+}$	$II$. $3d^3 4s^1$
$C$. $Ni^{2+}$	$III$. $3d^4$
$D$. $V^{+}$	$IV$. $3d^5 4s^1$

Choose the correct answer from the options given below:

Number of electrons in the penultimate shell of $d-$block elements.

Niobium $(Nb)$ and ruthenium $(Ru)$ have " $x$ " and " $y$ " number of electrons in their respective $4d$ orbitals. The value of $x+y$ is $...........$

Which of the following graphs is the correct representation of the relationship between atomic number $(Z)$ and the magnetic moment of $d-$block elements? [Outer electronic configuration : $(n - 1)d^x\ ns^{1\ or\ 2}$]

Choose the element which is not radioactive.