Identify the correct decreasing order of densities of $d-$block elements.

The correct order of density for the $3d$ series elements is:

The correct option with the order of melting points of the pairs $(Mn, Fe)$, $(Tc, Ru)$ and $(Re, Os)$ is $:$

In which of the following pairs,both the elements do not have $(n-1)d^{10} ns^2$ configuration?

Which of the following statements is correct regarding the ions $Zn^{2+}$,$Ni^{2+}$,and $Cr^{3+}$? (Atomic numbers: $Zn = 30$,$Ni = 28$,$Cr = 24$)

The magnetic nature of elements depends on the presence of unpaired electrons. Identify the configuration of transition elements which shows the highest magnetic moment.