Question

The correct order of following 3d metal oxides, according to their oxidation numbers is :
(a) $CrO_3$
(b) $Fe_2O_3$
(c) $MnO_2$
(d) $V_2O_5$
(e) $Cu_2O$

• (a) > (c) > (d) > (b) > (e)
• (a) > (d) > (c) > (b) > (e)
• (d) > (a) > (b) > (c) > (e)
• (c) > (a) > (d) > (e) > (b)

Hint:

Oxidation states in transition metal oxides usually correspond to the maximum valency for higher oxidation states (like Cr and V).

Answer 1

The Correct Option is B

To determine the correct order of the metal oxides based on their oxidation numbers, we need to calculate the oxidation state of the metal in each given oxide.

1. $CrO_3$: In chromium trioxide, oxygen has an oxidation number of -2. The overall charge is zero, so: x + 3(-2) = 0 \Rightarrow x - 6 = 0 \Rightarrow x = +6
   Thus, for $CrO_3$, the oxidation number of Cr is +6.
2. $Fe_2O_3$: In iron(III) oxide, the oxidation number of oxygen is -2. The overall charge is zero, so: 2x + 3(-2) = 0 \Rightarrow 2x - 6 = 0 \Rightarrow 2x = +6 \Rightarrow x = +3
   Thus, for $Fe_2O_3$, the oxidation number of Fe is +3.
3. $MnO_2$: In manganese dioxide, oxygen is -2. The overall charge is zero, so: x + 2(-2) = 0 \Rightarrow x - 4 = 0 \Rightarrow x = +4
   Thus, for $MnO_2$, the oxidation number of Mn is +4.
4. $V_2O_5$: In vanadium pentoxide, oxygen is -2. The overall charge is zero, so: 2x + 5(-2) = 0 \Rightarrow 2x - 10 = 0 \Rightarrow 2x = +10 \Rightarrow x = +5
   Thus, for $V_2O_5$, the oxidation number of V is +5.
5. $Cu_2O$: In copper(I) oxide, oxygen has an oxidation number of -2. The total charge is zero, so: 2x + (-2) = 0 \Rightarrow 2x = +2 \Rightarrow x = +1
   Thus, for $Cu_2O$, the oxidation number of Cu is +1.

Now, we can order the oxides by the oxidation numbers of their metals:

• $CrO_3$: +6
• $V_2O_5$: +5
• $MnO_2$: +4
• $Fe_2O_3$: +3
• $Cu_2O$: +1

The correct order based on oxidation numbers is: (a) > (d) > (c) > (b) > (e).

Hence, the correct answer is: (a) > (d) > (c) > (b) > (e).