Among following compounds, the number of those present in copper matte is ___________.

A. $$\mathrm{CuCO_{3}}$$

B. $$\mathrm{Cu_{2}S}$$

C. $$\mathrm{Cu_{2}O}$$

D. $$\mathrm{FeO}$$

The number of electrons involved in the reduction of permanganate to manganese dioxide in acidic medium is _____________.

How many of the following metal ions have similar value of spin only magnetic moment in gaseous state? ______________

(Given : Atomic number V, 23; Cr, 24; Fe, 26; Ni, 28)

V$$^{3+}$$, Cr$$^{3+}$$, Fe$$^{2+}$$, Ni$$^{3+}$$

The disproportionation of $$\mathrm{MnO}_{4}^{2-}$$ in acidic medium resulted in the formation of two manganese compounds $$\mathrm{A}$$ and $$\mathrm{B}$$. If the oxidation state of $$\mathrm{Mn}$$ in $$\mathrm{B}$$ is smaller than that of A, then the spin-only magnetic moment $$(\mu)$$ value of B in BM is __________. (Nearest integer)