The type of oxide formed by the element among Li, Na, Be, Mg, B and Al that has the least atomic radius is: (1) A_2O_3 (2) AO_2 (3) AO (4) A_2O

Solution & Explanation

### Core Logic Let's analyze the periodic trend among the listed elements: Li, Na, Be, Mg, B, Al. * Atomic radius decreases across a period due to increasing effective nuclear charge (Z_texteff). * Atomic radius increases down a group due to addition of electron shells. Comparing Period 2 elements (Li, Be, B): Boron (B) has the highest atomic number here and thus the smallest atomic radius. Boron forms an oxide where its oxidation state is +3, which gives B_2O_3. This matches the structural template A_2O_3. ### Pattern Recognition Smallest element in Period 2 (excluding noble gases) is on the far right. Boron belongs to Group 13, so it forms traditional trivalent acidic oxides (A_2O_3). ### Evaluation Rubric / Model Answer null ### Chapter Mix Class 11 Chemistry: Classification of Elements and Periodicity in Properties

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Classification Of Elements And Periodicity In Properties

More Classification of Elements and Periodicity in Properties Previous-Year Questions — Page 5

Q79 jee_main_2024_29_january_evening Electron Gain Enthalpy Trends
Given below are two statements: Statement I: Fluorine has most negative electron gain enthalpy in its group. Statement II: Oxygen has least negative electron gain enthalpy in its group. In the light of the above statements, choose the most appropriate from the options given below.
  • A. Both Statement I and Statement II are true.
  • B. Statement I is true but Statement II is false
  • C. Both Statement I and Statement II are false.
  • D. Statement I is false but Statement II is true.

Solution

### Related Formula Electron Gain Enthalpy (Delta_egH) trends in Group 16 and Group 17 elements. ### Core Logic Evaluating both statements: * **Statement I is false**: Due to its small size, strong inter-electronic repulsions in the compact 2p subshell of Fluorine limit incoming electrons compared to Chlorine. As a result, Chlorine (textCl) has the *most negative* electron gain enthalpy in Group 17. * **Statement II is true**: Similarly, the exceptionally small size of the Oxygen atom creates intense electron-electron repulsions. Consequently, it has the *least negative* electron gain enthalpy among all elements in Group 16. ### Step 1: Final Assessment Therefore, Statement I is false while Statement II is true, matching choice (4). ### Pattern Recognition Third-period elements (textCl, textS) exhibit more negative electron gain enthalpies than their second-period counterparts (textF, textO) due to lower inter-electronic repulsion in their larger valence shells. ### Evaluation Rubric / Model Answer null ### Chapter Mix Class 11 Chemistry: Classification of Elements and Periodicity
Q63 jee_main_2024_27_jan_morning Oxidation States
Element not showing variable oxidation state is:
  • A. Bromine
  • B. Iodine
  • C. Chlorine
  • D. Fluorine

Solution

### Core Logic Fluorine is the most electronegative element and lacks vacant d-orbitals in its valence shell. Consequently, it exhibits only a -1 oxidation state (and 0 in elemental form) and cannot show variable positive oxidation states unlike other halogens. ### Pattern Recognition First element of a group lacks d-orbitals rightarrow anomalous properties rightarrow Fluorine only exhibits -1. ### Chapter Mix Class 11 Chemistry: Classification of Elements and Periodicity in Properties
Q70 jee_main_2024_27_jan_morning S-block and F-block General Features
Given below are two statements: Statement (I): The 4f and 5f series of elements are placed separately in the Periodic table to preserve the principle of classification. Statement (II) : S-block elements can be found in pure form in nature. In the light of the above statements, choose the most appropriate answer from the options given below :
  • A. Statement I is false but Statement II is true
  • B. Both Statement I and Statement II are true
  • C. Statement I is true but Statement II is false
  • D. Both Statement I and Statement II are false

Solution

### Core Logic Statement I is true: The lanthanides (4textf) and actinides (5textf) are separated at the bottom of the periodic table to avoid distortion of the periodic trends layout and preserve clean structural classification groups. Statement II is false: s-block elements (alkali and alkaline earth metals) possess exceptionally low ionization energies, making them highly reactive; thus, they are always encountered as compounds rather than in native pure forms in nature. ### Chapter Mix Class 11 Chemistry: Classification of Elements and Periodicity in Properties
Q61 jee_main_2024_29_jan_morning Ionization Enthalpy
Given below are two statements : one is labelled as Assertion A and the other is labelled as Reason R: Assertion A: The first ionisation enthalpy decreases across a period. Reason R: The increasing nuclear charge outweighs the shielding across the period. In the light of the above statements, choose the most appropriate from the options given below:
  • A. textBoth A and R are true and R is the correct explanation of A
  • B. textA is true but R is false
  • C. textA is false but R is true
  • D. textBoth A and R are true but R is NOT the correct explanation of A

Solution

### Core Logic Assertion A states that the first ionisation enthalpy decreases across a period. This is false, because first ionisation energy generally increases along a period from left to right. Reason R states that the increasing nuclear charge outweighs the shielding across the period. This is true, and it is the exact reason why the atomic radius decreases and ionisation enthalpy increases across a period. ### Step 1: Final Conclusion Since the assertion is incorrect and the reason is a factually correct statement, A is false but R is true. ### Pattern Recognition Recall the horizontal periodic trends: across a period, effective nuclear charge (Z_texteff) dominates, pulling valence electrons tighter, increasing ionisation energy. ### Evaluation Rubric / Model Answer null ### Chapter Mix Class 11 Chemistry: Classification of Elements and Periodicity in Properties
Q73 jee_main_2024_30_january_evening Periodic Trends in Chemical Properties
Given below are two statements: Statement I: Along the period, the chemical reactivity of the element gradually increases from group 1 to group 18. Statement II: The nature of oxides formed by group 1 element is basic while that of group 17 elements is acidic. In the light above statements, choose the most appropriate from the questions given below:
  • A. textBoth statement I and Statement II are true.
  • B. textStatement I is true but Statement II is False.
  • C. textStatement I is false but Statement II is true.
  • D. textBoth Statement I and Statement II is false.

Solution

### Core Logic Statement I: Along a period, the chemical reactivity of elements first decreases and then increases. Group 1 elements (alkali metals) are highly reactive, Group 17 elements (halogens) are also highly reactive, but the elements in the middle (like carbon) are less reactive. Moreover, Group 18 elements (noble gases) are mostly inert. Therefore, statement I is false. Statement II: Group 1 elements are metals and form basic oxides (e.g., Na_2O). Group 17 elements are non-metals and form acidic oxides (e.g., Cl_2O_7). Therefore, statement II is true. ### Pattern Recognition Reactivity is highest at the extreme left (Group 1) and extreme right (Group 17) of the periodic table, excluding noble gases. Metallic character = basic oxides; Non-metallic character = acidic oxides. ### Evaluation Rubric / Model Answer null ### Chapter Mix Class 11 Chemistry: Classification of Elements and Periodicity in Properties

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