A transition metal ' $\mathrm{M}$ ' among $\mathrm{Sc}, \mathrm{Ti}, \mathrm{V}, \mathrm{Cr}, \mathrm{Mn}$ and $\mathrm{Fe}$ has the highest second ionisation enthalpy. The spin only magnetic moment value of $\mathrm{M}^{+}$ion is. . . . . . .$\mathrm{BM}$ (Near integer)

(Given atomic number $\mathrm{Sc}: 21, \mathrm{Ti}: 22, \mathrm{~V}: 23, \mathrm{Cr}$ : $24, \mathrm{Mn}: 25, \mathrm{Fe}: 26)$

Ionisation potential values of $d-$ block elements as compared to ionization potential value of $ f-$ block elements are

The melting point of $Zn$ is lower as compared to those of the other elements of $3d$ series because

Many transition metals form interstitial compounds. The characteristics of these interstitial compounds are

$(I)$ They have high melting points, higher than those of pure metals

$(II)$ They are very hard

$(III)$ They retain metallic conductivity

$(IV)$ They are chemically more reactive than the pure metals

The form of iron having the highest carbon content is

In the following members of transition elements, the lowest ionization energy is of