Which of the following pairs of elements does $NOT$ represent chemical twins?

Which of the following ions is diamagnetic?

To which block does the element with atomic number $106$ belong?

The number of $d$-electrons in $Cr^{3+}$ ion $(Z=24)$ is

The atomic number of $Pd$ is $46$. The atomic numbers of the elements lying immediately above and below it in the same group are,respectively,.....................

Which forms coloured salts?