Question #44855

A 3d transition metal $M$ exhibits a positive standard reduction potential $E^\circ(M^{2+}/M) = +0.34\text{ V}$ at $298\text{ K}$ because its hydration enthalpy fails to compensate for the sum of its atomization and ionization enthalpies. When an aqueous solution of $M^{2+}$ is treated with excess $KCN(aq)$, a soluble coordination complex $\mathbf{X}$ and a toxic gas $\mathbf{Y}$ are formed. Separately, when $M^{2+}(aq)$ is treated with excess $KI(aq)$, a precipitate $\mathbf{Z}$ and a brown solution containing species $\mathbf{W}$ are formed.

Determine the value of the expression: $(p \times r) + s - q$ Where: $p$ = Coordination number of the central metal in complex $\mathbf{X}$ $q$ = Number of unpaired electrons in the central metal of complex $\mathbf{X}$ $r$ = Oxidation state of $M$ in precipitate $\mathbf{Z}$ $s$ = Atomicity (total number of atoms per molecule) of gas $\mathbf{Y}$