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

To the free end of a spring hanging from a rigid support,a block of mass $m$ is hung and slowly allowed to come to its equilibrium position. Then the stretching in the spring is $d$. If the same block is attached to the same spring and allowed to fall suddenly,the amount of stretching is: (force constant,$k$)

The structure of $XeOF_4$ is

The electronic configurations of $Eu$ (Atomic No $63$),$Gd$ (Atomic No $64$) and $Tb$ (Atomic No $65$) are

Which of the following has the maximum nucleophilicity?

Match the following columns:

Column-$I$	Column-$II$
$a$. Bicuspid valve	$p$. Brain
$b$. Nephron	$q$. Liver
$c$. Alveoli	$r$. Heart
$d$. Cerebrum	$s$. Kidney
	$t$. Lungs