Which of the following pairs of elements have one electron in the $5d$-subshell in their observed electronic configuration?

Calculate the number of unpaired electrons in the following gaseous ions: $Mn^{3+}, Cr^{3+}, V^{3+}$ and $Ti^{3+}$. Which one of these is the most stable in aqueous solution?

Given below are two statements: one is labelled as Assertion $(A)$ and the other is labelled as Reason $(R)$.
Assertion $(A)$: The first ionization enthalpy of $3d$ series elements is more than that of group $2$ metals.
Reason $(R)$: In $3d$ series of elements,successive filling of $d$-orbitals takes place.
In the light of the above statements,choose the correct answer from the options given below:

Which of the following pairs of ions have the same paramagnetic moment?

The most abundant transition metal in the earth's crust is

What is the value of the spin-only magnetic moment of $Ni$ $(Z=28)$ in the $+2$ oxidation state (in $BM$)?