Identify the metal that forms colourless compounds.

Which element from the following exhibits the highest number of various different possible oxidation states?

How many of the following lanthanide elements exhibit $+4$ oxidation state?
$Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy$

Assertion: In general,transition metals have high melting points.
Reason: More number of electrons from $(n-1)d$ and $ns$ are involved in interatomic metallic bonding.
The correct option among the following is

The $d-$block element which is a liquid at room temperature,has a high specific heat,lower reactivity than hydrogen,and its chloride $(MX_2)$ is volatile on heating is

The correct order of ionic radii of $Y^{3+}$,$La^{3+}$,$Eu^{3+}$ and $Lu^{3+}$ is
(Atomic No. $Y = 39$,$La = 57$,$Eu = 63$,$Lu = 71$)