d and f Block Elements JEE Main previous year questions with solutions

5 solved JEE Main questions on d and f Block Elements, free to read — no sign-in needed. The full chapter has 266 questions; sign in to attempt the remaining 261 in the exam simulator.

1. Q1JEE Main 2026 (05 Apr, Shift 2)Compounds of Transition Metals
   A paper dipped in a dil. $H_2SO_4$ solution of '$X$' upon treatment with $SO_2$ gas turns into green. The compound '$X$' is :
   1. A.KI-starch
   2. B.$KMnO_4$
   3. C.$Pb(CH_3COO)_2$
   4. D.$K_2Cr_2O_7$
   Show answer & solution

   Answer: (D)

   $SO_2$ gas acts as a reducing agent. When a paper dipped in an acidified solution of potassium dichromate ($K_2Cr_2O_7$) is exposed to $SO_2$ gas, the orange-colored dichromate ion ($Cr_2O_7^{2-}$) is reduced to the green-colored chromium(III) ion ($Cr^{3+}$). The chemical reaction is: $K_2Cr_2O_7 + H_2SO_4 + 3SO_2 \rightarrow K_2SO_4 + Cr_2(SO_4)_3 + H_2O$ The formation of chromium(III) sulfate, $Cr_2(SO_4)_3$, is responsible for the green color. Thus, the compound '$X$' is $K_2Cr_2O_7$. Answer: $K_2Cr_2O_7$
2. Q2JEE Main 2025 (04 Apr, Shift 2)F-Block elements
   The incorrect relationship in the following pairs in relation to ionisation enthalpies is :
   1. A.$\mathrm{Mn}^{+} \lt \mathrm{Cr}^{+}$
   2. B.$\mathrm{Mn}^{+} \lt \mathrm{Mn}^{2+}$
   3. C.$\mathrm{Fe}^{2+} \lt \mathrm{Fe}^{3+}$
   4. D.$\mathrm{Mn}^{2+} \lt \mathrm{Fe}^{2+}$
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   Answer: (D)

   $\mathrm{Mn}^{2+}:[\mathrm{Ar}] 3 \mathrm{~d}^5$ Half filled stability More 1 E than $\mathrm{Fe}^{2+}$ $\mathrm{Fe}^{2+}:[\mathrm{Ar}] 3 \mathrm{~d}^6$
3. Q3JEE Main 2024 (06 Apr, Shift 2)Electron displacement effects
   Among $\mathrm{VO}_2^{+}, \mathrm{MnO}_4^{-}$and $\mathrm{Cr}_2 \mathrm{O}_7^{2-}$, the spin-only magnetic moment value of the species with least oxidising ability is ______ BM (Nearest integer). (Given atomic member $\mathrm{V}=23, \mathrm{Mn}=25, \mathrm{Cr}=24$)
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   Answer: 0

   For 3d transition series; Oxidising power : $\mathrm{V}^{+5} \lt \mathrm{Cr}^{+6} \lt \mathrm{Mn}^{+7}$ $\mathrm{V}^{+5}:[\mathrm{Ar}] 4 \mathrm{~s}^0 3 \mathrm{~d}^0$ Number of unpaired electron $=0$ $\mu=0$
4. Q4JEE Main 2023 (12 Apr, Shift 1)Electronic configuration
   Given below are two statement : one is labelled as Assertion A and the other is labelled as Reason R Assertion A : $5f$ electron can participate in bonding to a far greater extent than $4f$ electrons Reason R : $5f$ orbitals are not as buried as $4f$ orbitals In the light of the above statements, choose the correct answer from the options given below
   1. A.A is false but R is true
   2. B.Both A and R are true and R is the correct explanation of A
   3. C.A is true but R is false
   4. D.Both A and R are true but R is NOT the correct explanation of A
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   Answer: (B)

   The distance between the nucleus and 5f orbital is more than the distance between the nucleus and 4f orbital. Hence the hold of nucleus on valence electron decrease in 5f orbital. 5f orbital not buried as 4f oribitals so electron present in 5f orbital experience less nuclear attraction than electron present in 4f orbital. Hence electrons of 5f orbital can take part in bonding to far great extent.
5. Q5JEE Main 2022 (29 Jul, Shift 2)Properties of D-block elements
   Which of the following $3d-metal$ ion will give the lowest enthalpy of hydration $\left({\Delta }_{hyd}H\right)$ when dissolved in water?
   1. A.${Cr}^{2+}$
   2. B.${Mn}^{2+}$
   3. C.${Fe}^{2+}$
   4. D.${Co}^{2+}$
   Show answer & solution

   Answer: (B)

   Hydration enthalpy (ꕔHHyd) is the change in enthalpy when one mole of gaseous ion under a standard condition of 1 bar pressure dissolves in a sufficient amount of water to form an infinitely dilute solution (infinite dilution means a further addition of solute will not cause any heat change). Hydration enthalpy is inversely related to the size of the ion, smaller the size of the ion greater is the hydration and hence greater is the hydration energy released. Mn+2 has the lowest hydration energy among the given ions as it has the largest size. Ion ${\Delta H}_{Hyd.}^{o}(kJ/mole)$ ${Cr}^{2+}$ $-1925$ ${Mn}^{2+}$ $-1862$ ${Fe}^{2+}$ $-1998$ ${Co}^{2+}$ $-2079$