d – d transition

L $$\to$$ M charge transfer transition

$$\sigma$$ – $$\sigma$$* transition

M $$\to$$ L charge transfer transition

$$\left( A \right) - \left( {ii} \right),\,\,\left( B \right) - \left( {iii} \right),\,\,\left( C \right) - \left( {iv} \right),\,\,\left( D \right) - \left( i \right)$$

$$\left( A \right) - \left( {iii} \right),\,\,\left( B \right) - \left( i \right),\,\,\left( C \right) - \left( {ii} \right),\,\,\left( D \right) - \left( {iv} \right)$$

$$\left( A \right) - \left( {iii} \right),\,\,\left( B \right) - \left( {ii} \right),\,\,\left( C \right) - \left( {iv} \right),\,\,\left( D \right) - \left( i \right)$$

$$\left( A \right) - \left( {ii} \right),\,\,\left( B \right) - \left( i \right),\,\,\left( C \right) - \left( {iv} \right),\,\,\left( D \right) - \left( {iii} \right)$$

Fe $$\buildrel {dil.\,{H_2}S{O_4}} \over \longrightarrow $$ FeSO₄ $$\buildrel {{H_2}S{O_4},{O_2}} \over \longrightarrow $$ Fe₂(SO₄)₃ $$\buildrel {heat} \over \longrightarrow $$ Fe

Fe $$\buildrel {{O_2} \, {, heat}} \over \longrightarrow $$ FeO $$\buildrel {dil.\,{H_2}S{O_4}} \over \longrightarrow $$ FeSO₄ $$\buildrel {heat} \over \longrightarrow $$ Fe

Fe $$\buildrel {{Cl_2} \, {, heat}} \over \longrightarrow $$ FeCl₃ $$\buildrel {heat, \, air} \over \longrightarrow $$ FeCl₂ $$\buildrel {Zn} \over \longrightarrow $$ Fe

Fe $$\buildrel {{O_2},\,heat} \over \longrightarrow $$ Fe₃O₄ $$\buildrel {CO,\,{{600}^o}C} \over \longrightarrow $$ FeO $$\buildrel {CO,\,{{700}^o}C} \over \longrightarrow $$ Fe

Ni²⁺ < Co²⁺ < Fe²⁺ < Mn²⁺ : ionic size

Co³⁺ < Fe³⁺ < Cr³⁺ < Sc³⁺ : stability in aqueous solution

Sc < Ti < Cr < Mn : number of oxidation states

V²⁺ < Cr²⁺ < Mn²⁺ < Fe²⁺ : paramagnetic behaviour