JEE Chemistry 2025 Question with Solution

Given: We need the number of acidic oxides among $VO_2, V_2O_3, CrO_3, V_2O_5$ and $Mn_2O_7$, and the primary valency of cobalt in $[Co(H_2NCH_2CH_2NH_2)_3]_2 (SO_4)_3$.

Find: The value of $X + Y$.

For transition metal oxides, acidic character generally increases with oxidation state.

From the extracted solution:

• $VO_2$ : amphoteric
• $V_2O_3$ : basic
• $CrO_3$ : acidic
• $V_2O_5$ : amphoteric, predominantly acidic
• $Mn_2O_7$ : highly acidic

The solution finally counts the acidic oxides as $CrO_3$ and $Mn_2O_7$ only, so

$$X = 2$$

Now consider $[Co(H_2NCH_2CH_2NH_2)_3]_2 (SO_4)_3$. The ligand ethylenediamine is neutral, and the compound contains the complex ion $[Co(en)_3]^{3+}$.

Let the oxidation state of cobalt be $y$. Then

$$y + 3(0) = +3$$ $$y = +3$$

So the primary valency of cobalt is

$$Y = 3$$

Therefore,

$$X + Y = 2 + 3 = 5$$

The correct option is A.

The solution contains an internal discrepancy in one approach, but the final consistent worked answer on the page is $5$.

Given: The oxides are $VO_2, V_2O_3, CrO_3, V_2O_5$ and $Mn_2O_7$, and the complex is $[Co(H_2NCH_2CH_2NH_2)_3]_2 (SO_4)_3$.

Find: $X + Y$.

Step 1: Identify acidic oxides. Higher oxidation states of transition metals generally give more acidic oxides.

• In $VO_2$, vanadium is in oxidation state $+4$, and the extracted solution labels it amphoteric.
• In $V_2O_3$, vanadium is in oxidation state $+3$, and the extracted solution labels it basic.
• In $CrO_3$, chromium is in oxidation state $+6$, so it is acidic.
• In $V_2O_5$, vanadium is in oxidation state $+5$; the extracted solution describes it as amphoteric, predominantly acidic, but does not include it in the final count.
• In $Mn_2O_7$, manganese is in oxidation state $+7$, so it is highly acidic.

Thus the page's final accepted count is

$$X = 2$$

Step 2: Find the primary valency of cobalt. In $[Co(H_2NCH_2CH_2NH_2)_3]_2 (SO_4)_3$, ethylenediamine is a neutral ligand. Sulfate is $SO_4^{2-}$, and there are three sulfate ions, giving total negative charge

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

Hence the two complex cations together must contribute $+6$, so each complex cation has charge $+3$:

$$[Co(en)_3]^{3+}$$

Therefore cobalt has oxidation state

$$Y = 3$$

Step 3: Add the values.

$$X + Y = 2 + 3 = 5$$

Therefore, the correct option is A.