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d- and f-Block Elements

JEE Main 2026 (Online) 21st January Morning ShiftNumericalMedium📈 Topic in 19% papers+4
Ques. 1JEE Main 2026, 21 January (Morning Shift)

Consider the following reactions : NaCl + K2Cr2O7 + H2SO4 A + KHSO4 + NaHSO4 + H2O A + NaOH B + NaCl + H2O B + H2SO4 + H2O2 C + Na2SO4 + H2O In the product 'C', 'X' is the number of O22- units, 'Y' is the total number of oxygen atoms present and 'Z' is the oxidation state of Cr. The value of X + Y + Z is .

Answer

13

Solution

The first step is the chromyl chloride test:

4NaCl + K2Cr2O7 + 6H2SO4 2CrO2Cl2 + 2KHSO4 + 4NaHSO4 + 3H2O

so A = CrO2Cl2 (chromyl chloride). With NaOH it gives yellow sodium chromate, so B = Na2CrO4:

CrO2Cl2 + 4NaOH Na2CrO4 + 2NaCl + 2H2O

Acidified H2O2 then gives the blue chromium peroxide, so C = CrO5:

Na2CrO4 + H2SO4 + 2H2O2 CrO5 + Na2SO4 + 3H2O

CrO5 has a butterfly structure with one Cr=O and two peroxo O22- groups, so X = 2 and Y = 5.

Oxidation state of Cr: Z + (−2) + 2(−2) = 0 Z = +6

X + Y + Z = 2 + 5 + 6 = 13

Answer: 13

Keep practising — d- and f-Block Elements

Ques. 2JEE Main 2026, 21 January (Evening Shift)

Given below are some of the statements about Mn and Mn2O7. Identify the correct statements. Choose the correct answer from the options given below :

  1. A, B, C and D
  2. A, B and D Only
  3. A, B and C Only
  4. A, C and D Only
Ques. 3JEE Main 2025, 8 April (Evening Shift)

The correct decreasing order of spin only magnetic moment values (BM) of Cu+, Cu2+, Cr2+ and Cr3+ ions is :

  1. Cr3+ > Cr2+ > Cu+ > Cu2+
  2. Cu+ > Cu2+ > Cr3+ > Cr2+
  3. Cr2+ > Cr3+ > Cu2+ > Cu+
  4. Cu2+ > Cu+ > Cr2+ > Cr3+
Ques. 4JEE Main 2025, 7 April (Morning Shift)

The first transition series metal 'M' has the highest enthalpy of atomisation in its series. One of its aquated ions ( Mn+) exists in green colour. The nature of the oxide formed by the above Mn+ ion is:

  1. basic
  2. neutral
  3. amphoteric
  4. acidic
Ques. 5JEE Main 2025, 7 April (Morning Shift)

The number of valence electrons present in the metal among Cr, Co, Fe and Ni which has the lowest enthalpy of atomisation is :

  1. 10
  2. 6
  3. 9
  4. 8
Ques. 6JEE Main 2025, 7 April (Evening Shift)

'X' is the number of acidic oxides among VO2, V2O3, CrO3, V2O5 and Mn2O7. The primary valency of cobalt in [Co(H2NCH2CH2NH2)3]2(SO4)3 is Y. The value of X + Y is .

  1. 3
  2. 4
  3. 2
  4. 5
Ques. 7JEE Main 2025, 4 April (Morning Shift)

Pair of transition metal ions having the same number of unpaired electrons is

  1. Ti3+, Mn2+
  2. Ti2+, Co2+
  3. Fe3+, Cr2+
  4. V2+, Co2+
Ques. 8JEE Main 2025, 4 April (Morning Shift)

KMnO4 acts as an oxidising agent in acidic medium. 'X' is the difference between the oxidation states of Mn in reactant and product. 'Y' is the number of 'd' electrons present in the brown red precipitate formed at the end of the acetate ion test with neutral ferric chloride. The value of X + Y is .

Ques. 9JEE Main 2025, 4 April (Evening Shift)

The incorrect relationship in the following pairs in relation to ionisation enthalpies is :

  1. Mn2+ < Fe2+
  2. Mn+ < Mn2+
  3. Mn+ < Cr+
  4. Fe2+ < Fe3+
Ques. 10JEE Main 2025, 3 April (Morning Shift)

The metal ions that have the calculated spin-only magnetic moment value of 4.9 B.M. are : Choose the correct answer from the options given below:

  1. A, D and E Only
  2. A, B and E Only
  3. A, C and E Only
  4. B and E Only
Ques. 11JEE Main 2025, 3 April (Morning Shift)

Consider the following reactions A + Little amountNaCl + H2SO4 CrO2Cl2 + Side Products CrO2Cl2(Vapour) + NaOH B + NaCl + H2O B + H+ C + H2O The number of terminal 'O' present in the compound 'C' is

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