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Classification of Elements and Periodicity in Properties

JEE Main 2026 (Online) 22nd January Morning ShiftMCQMedium📈 Topic in 32% papers+4−1
Ques. 1JEE Main 2026, 22 January (Morning Shift)

A 'p'-block element (E) and hydrogen form a binary cation (EHx)+, while EH3 on treatment with K2HgI4 in alkaline medium gives a precipitate of basic mercury(II) amido-iodine. Given below are first ionisation enthalpy values ( kJ mol-1) for first element each from group 13, 14, 15 and 16. Identify the correct first ionisation enthalpy value for element E.

  1. 1402
  2. 1086
  3. 801
  4. 1312

Answer

(1) 1402

Solution

Alkaline K2HgI4 is Nessler's reagent; it gives a brown precipitate of basic mercury(II) amido-iodine with ammonia.

EH3 = NH3 and the cation (EHx)+ = NH4+ E = N (first element of group 15).

First ionisation enthalpies ( kJ mol-1): B 801, C 1086, N 1402, O 1314 (≈ 1312).

N has the stable half-filled 2p3 configuration its ionisation enthalpy is even higher than that of O.

For E (nitrogen), iH1 = 1402 kJ mol-1

Answer: (1)

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Ques. 2JEE Main 2026, 22 January (Evening Shift)

Given below are two statements : In the light of the above statements, choose the correct answer from the options given below :

  1. Both Statement I and Statement II are false
  2. Statement I is false but Statement II is true
  3. Statement I is true but Statement II is false
  4. Both Statement I and Statement II are true
Ques. 3JEE Main 2026, 21 January (Morning Shift)

Which of the following represents the correct trend for the mentioned property? Choose the correct answer from the options given below :

  1. B and C only
  2. A, B and D only
  3. A and B only
  4. A, B, C and D
Ques. 4JEE Main 2026, 21 January (Evening Shift)

Given below are two statements : In the light of the above statements, choose the correct answer from the options given below :

  1. Statement I is true but Statement II is false
  2. Both Statement I and Statement II are true
  3. Statement I is false but Statement II is true
  4. Both Statement I and Statement II are false
Ques. 5JEE Main 2025, 8 April (Evening Shift)

The atomic number of the element from the following with lowest 1st ionisation enthalpy is :

  1. 32
  2. 35
  3. 19
  4. 87
Ques. 6JEE Main 2025, 7 April (Evening Shift)

Choose the incorrect trend in the atomic radii (r) of the elements.

  1. rRb < rCs
  2. rAt < rCs
  3. rBr < rK
  4. rMg < rAl
Ques. 7JEE Main 2025, 3 April (Morning Shift)

Which of the following statements are correct? Choose the correct answer from the options given below:

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

Match the LIST-I with LIST-II Choose the correct answer from the options given below:

  1. A-IV, B-I, C-II, D-III
  2. A-IV, B-III, C-I, D-II
  3. A-III, B-I, C-IV, D-II
  4. A-II, B-III, C-IV, D-I
Ques. 9JEE Main 2025, 2 April (Evening Shift)

Electronic configuration of four elements A, B, C and D are given below: (A) 1s2 2s2 2p3 (B) 1s2 2s2 2p4 (C) 1s2 2s2 2p5 (D) 1s2 2s2 2p2 Which of the following is the correct order of increasing electronegativity (Pauling's scale)?

  1. D < A < B < C
  2. A < B < C < D
  3. A < C < B < D
  4. A < D < B < C
Ques. 10JEE Main 2025, 29 January (Morning Shift)

Given below are two statements : In the light of the above statements, choose the most appropriate answer from the options given below :

  1. Statement I is incorrect but Statement II is correct
  2. Both Statement I and Statement II are correct
  3. Statement I is correct but Statement II is incorrect
  4. Both Statement I and Statement II are incorrect
Ques. 11JEE Main 2025, 29 January (Evening Shift)

The type of oxide formed by the element among Li, Na, Be, Mg, B and Al that has the least atomic radius is :

  1. AO
  2. AO2
  3. A2O
  4. A2O3

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