Question

'X' is the number of acidic oxides among $ VO_2, V_2O_3, CrO_3, V_2O_5 $ and $ Mn_2O_7 $. The primary valency of cobalt in $ [Co(H_2NCH_2CH_2NH_2)_3]_2 (SO_4)_3 $ is Y. The value of X + Y is :

• A. 5
• B. 4
• C. 2
• D. 3

Hint:

Remember the trends in the acidic/basic nature of metal oxides with respect to the oxidation state of the metal. Higher oxidation states tend to be more acidic. Primary valency in coordination complexes refers to the oxidation state of the central metal ion.

Answer 1

The Correct Option is A

Step 1: Determine the acidic oxides among the given options.
The acidic character of transition metal oxides increases with the oxidation state of the metal.
\( VO_2 \): Oxidation state of V is +4 (amphoteric) \( V_2O_3 \): Oxidation state of V is +3 (basic) \( CrO_3 \): Oxidation state of Cr is +6 (acidic) \( V_2O_5 \): Oxidation state of V is +5 (amphoteric, predominantly acidic) \( Mn_2O_7 \): Oxidation state of Mn is +7 (highly acidic) The acidic oxides are \( CrO_3 \) and \( Mn_2O_7 \). The number of acidic oxides, X = 2.
Step 2: Determine the primary valency of cobalt in the given complex.
The complex is \( [Co(H_2NCH_2CH_2NH_2)_3]_2 (SO_4)_3 \), which contains the complex ion \( [Co(en)_3]^{3+} \). The primary valency is the oxidation state of the central metal ion (Co). Let the oxidation state of Co be \( y \). Ethylenediamine (en) is a neutral ligand. \( y + 3(0) = +3 \) \( y = +3 \)
The primary valency of cobalt (Y) is 3.
Step 3: Calculate the value of X + Y.
X = 2
Y = 3
X + Y = 2 + 3 = 5