The spin-only magnetic moment value of $\mathrm{M}^{\mathrm{n}+}$ ion formed among $\mathrm{Ni}, \mathrm{Zn}, \mathrm{Mn}$ and Cu that has the least enthalpy of atomisation is_________ . (in nearest integer) Here n is equal to the number of diamagnetic complexes among $\mathrm{K}_2\left[\mathrm{NiCl}_4\right],\left[\mathrm{Zn}\left(\mathrm{H}_2 \mathrm{O}\right)_6\right] \mathrm{Cl}_2$, $\mathrm{K}_3\left[\mathrm{Mn}(\mathrm{CN})_6\right]$ and $\left[\mathrm{Cu}\left(\mathrm{PPh}_3\right)_3 \mathrm{I}\right]$

<p>$\mathrm{K}_2\left[\mathrm{NiCl}_4\right] \Rightarrow \mathrm{sp}^3$, Paramagnetic</p> <p>$\left[\mathrm{Zn}\left(\mathrm{H}_2 \mathrm{O}\right)_6\right] \mathrm{Cl}_2 \Rightarrow \mathrm{sp}^3 \mathrm{~d}^2$, Diamagnetic</p> <p>$\mathrm{K}_3\left[\mathrm{Mn}(\mathrm{CN})_6\right] \Rightarrow \mathrm{d}^2 \mathrm{sp}^3$, Paramagnetic</p> <p>$\left[\mathrm{Cu}\left(\mathrm{PPh}_3\right)_3 \mathrm{I}\right] \Rightarrow \mathrm{sp}^3$, Diamagnetic</p> <p>Hence the value of $n$ is 2</p> <p>Least value of enthalpy of atomisation among Ni,</p> <p>$\mathrm{Zn}, \mathrm{Mn}$ and Cu is of Zn</p> <p>$$\begin{aligned} & \mathrm{Zn}^{+2}:-[\mathrm{Ar}] 3 \mathrm{~d}^{10} \\ & \mu=0 \end{aligned}$$</p>