Acidic Oxides and Primary Valency of Cobalt

❓ Question

• ‘X’ is the number of acidic oxides among: VO₂, V₂O₃, CrO₃, V₂O₅, Mn₂O₇.

• The primary valency of cobalt in the complex
  $[ \mathrm{Co}(\mathrm{H_2NCH_2CH_2NH_2})_3 ]_2(\mathrm{SO_4})_3$
  (i.e. $[Co(\text{en})_3]_2(SO_4)_3$) is ‘Y’.

Find the value of X + Y.

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🖼️ Question Image

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✍️ Short Explanation

This problem is based on:

👉 Acidic/basic nature of oxides
👉 Werner theory
👉 Primary valency.

Main idea:

• Higher oxidation state metal oxides are generally acidic.
• Primary valency = oxidation state of central metal ion.

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🔷 Step 1 — Identify Acidic Oxides 💯

$VO_2$

Vanadium oxidation state:

$$+4$$

This oxide is amphoteric.

❌ Not purely acidic.

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$V_2O_3$

Vanadium oxidation state:

$$+3$$

Basic oxide.

❌ Not acidic.

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$CrO_3$

Chromium oxidation state:

$$+6$$

Strongly acidic oxide.

✔ Acidic.

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$V_2O_5$

Vanadium oxidation state:

$$+5$$

Acidic oxide.

✔ Acidic.

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$Mn_2O_7$

Manganese oxidation state:

$$+7$$

Strongly acidic oxide.

✔ Acidic.

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Thus acidic oxides are:

$$CrO_3,\ V_2O_5,\ Mn_2O_7$$

Hence:

$$\boxed{ X=3 }$$

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🔷 Step 2 — Find Primary Valency of Co

Compound:

$$[Co(en)_3]_2(SO_4)_3$$

where:

$$en = H_2NCH_2CH_2NH_2$$

is neutral ligand.

Sulfate charge:

$$3\times(-2)=-6$$

Hence total charge on two complex ions:

$$+6$$

Therefore each complex ion charge:

$$+3$$

So oxidation state of Co:

$$\boxed{ +3 }$$

Primary valency:

$$\boxed{ Y=3 }$$

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🔷 Step 3 — Calculate $X+Y$

$$X+Y=3+3$$
$$\boxed{ 6 }$$

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🔷 Step 4 — Important Observation 🚨

The calculated answer is:

$$\boxed{ 6}$$

but this value is not present in given options.

Hence:

✔ Either question/options contain printing error

✔ Or one oxide was intended differently.

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✅ Final Answer

$$\boxed{{\displaystyle 6}}$$

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