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d- and f-Block Elements · Question 23

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

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

Chromyl chloride test:

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

A = CrO2Cl2 (chromyl chloride)

CrO2Cl2 + 4NaOH Na2CrO4 + 2NaCl + 2H2O

B = Na2CrO4 (yellow)

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

C = CrO5 (blue chromium peroxide, butterfly structure: one Cr=O and two peroxo O22- groups)

X = 2, Y = 5

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

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

Answer: 13

JEE Main 2026 (Online) 21st January Morning Shift

Keep practising — d- and f-Block Elements

2

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
JEE Main 2026 (Online) 21st January Evening Shift
3

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+
JEE Main 2025 (Online) 8th April Evening Shift
4

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
JEE Main 2025 (Online) 7th April Morning Shift
5

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
JEE Main 2025 (Online) 7th April Morning Shift
6

'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
JEE Main 2025 (Online) 7th April Evening Shift
7

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+
JEE Main 2025 (Online) 4th April Morning Shift
8

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 .

JEE Main 2025 (Online) 4th April Morning Shift
9

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+
JEE Main 2025 (Online) 4th April Evening Shift
10

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
JEE Main 2025 (Online) 3rd April Morning Shift
11

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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