- A$C{u^ + }$
- B$Z{n^{ + 2 }}$
- C$A{g^ + }$
- ✓$F{e^{ + 2 }}$
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$\left( {{C_2}O_4^{2 - } = } \right.$ Oxalato $)$
$[E (en)_2 (C_2O_4)]NO_2$ (where $(en)$ is ethylene diamine) are, respectively,

$(1)$ $Fe^{3+}$ gives brown colour with potassium ferricyanide
$(2)$ $Fe^{2+}$ gives blue colour with potassium ferricyanide
$(3)$ $Fe^{3+}$ gives red colour with potassium thiocyanate
$(4)$ $Fe^{2+}$ gives brown colour with ammonium thiocyanate
$F{e^{3 + }}(aq) + {e^ - } \to F{e^{ - 1}}(aq);\,{E^o} = + 0.77\,V$
$A{l^{3 + }}(aq) + 3{e^ - } \to Al(s);\,{E^o} = - 1.66\,V$
$B{r_2}(aq) + 2{e^ - } \to 2B{r^ - }(aq);\,{E^o} = + 1.08\,V$
Based on the data given above, reducing power of $F{e^{2 + }},\,Al$ and $B{r^ - }$ will increase in the order