Misch metal is an alloy of $:-$

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:

In the periodic table,the first transition series is placed in:

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

Which of the following statements is incorrect?

Explain $d$-block elements of the periodic table.