Identify the correct order of atomic radii for the following $3d$ series elements.

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

In the ground state of cobalt atom $(Z = 27)$ there are $.......$ unpaired electrons and thus the atom is $.......$

Observe the following statements:
$a$) The basic strength of $Lu(OH)_3$,$Gd(OH)_3$ and $Ce(OH)_3$ follows the order: $Ce(OH)_3 > Gd(OH)_3 > Lu(OH)_3$
$b$) $O^{2-}$,$N^{3-}$,$F^{-}$ and $Na^{+}$ are isoelectronic species
$c$) The sizes of $Zr$ and $Hf$ are approximately the same
The correct statements are:

Which of the following is not a characteristic of transition elements?

Which element from the following in $+3$ oxidation state forms colourless compounds?