Chemistry Q59 – JEE-MAIN 2026

Home Chemistry Periodicity & ElementsQuestion #528

Given below are two statements: Statement I: Aluminium is more electropositive than thallium as the standard electrode potential value of

E_{A l^{3 +} / A l}^{\circ}

is negative and

E_{T l^{3 +} / T l}^{\circ}

is positive. Statement II: The sum of first three ionization enthalpies of boron is very high when compared to that of aluminium. Due to this reason boron forms covalent compounds only and aluminium forms

A l^{3 +}

ion. In the light of the above statements, choose the correct answer from the options given below

Clue 1 of 3: Electropositivity and Ionization Enthalpy Trends

Recall the periodic trends for electropositivity and ionization enthalpy within a group, especially for Group 13 elements.

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Step 1: Evaluate Statement I (Electropositivity)✦ Active

Electropositivity is the tendency of an element to lose electrons. A more negative standard reduction potential ( $E^{\circ}$ ) indicates a greater tendency to be oxidized, hence higher electropositivity. For Aluminium, $E_{A l^{3 +} / A l}^{\circ}$ is approximately $- 1.66 V$ (negative). For Thallium, $E_{T l^{3 +} / T l}^{\circ}$ is approximately $+ 0.72 V$ (positive). Since Aluminium has a more negative standard reduction potential, it is more electropositive than Thallium. Thus, Statement I is true.

Step 2: Evaluate Statement II (Ionization Enthalpy and Bonding)○ Expand

The sum of the first three ionization enthalpies of Boron is significantly higher than that of Aluminium due to Boron's smaller size and higher effective nuclear charge. This high ionization enthalpy makes the formation of $B^{3 +}$ ions energetically unfavorable, leading Boron to primarily form covalent compounds. For Aluminium, the sum of ionization enthalpies is lower (compared to Boron), allowing it to form $A l^{3 +}$ ions in some compounds (e.g., $A l F_{3}$ ), although it also forms covalent compounds (e.g., $A l C l_{3}$ ). The statement accurately links the difference in ionization enthalpies to the observed bonding characteristics. Thus, Statement II is true.

Step 3: Combine Conclusions○ Expand

Since both Statement I and Statement II are true, the correct option is the one stating that both statements are true.

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Chemistry Question 59 – JEE-MAIN 2026

Clue 1 of 3: Electropositivity and Ionization Enthalpy Trends

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