Chemistry Q60 – JEE-MAIN 2025

Home Chemistry Periodicity & ElementsQuestion #533

Which of the following statements are correct ? A. The process of adding an electron to a neutral gaseous atom is always exothermic. B. The process of removing an electron from an isolated gaseous atom is always endothermic. C. The

1^{s t}

ionization energy of boron is less than that of beryllium. D. The electronegativity of C is 2.5 in

C H_{4}

and

C C l_{4}

. E. Li is the most electropositive among elements of group I. Choose the correct answer from the options given below:

Clue 1 of 3: Fundamental Definitions

Recall the definitions and general trends for electron gain enthalpy, ionization energy, electronegativity, and electropositivity across periods and down groups.

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Ninja Strategy•Eliminate Obvious Falsehoods

Quickly identify and eliminate statements that are clearly false based on fundamental periodic trends and exceptions (e.g., electron gain enthalpy not always exothermic, electropositivity trend in a group).

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Step 1: Evaluate Statements A and B (Electron Gain Enthalpy and Ionization Energy)✦ Active

Statement A: "The process of adding an electron to a neutral gaseous atom is always exothermic." This is incorrect. Electron gain enthalpy (or electron affinity) can be endothermic for elements like noble gases, alkaline earth metals, and nitrogen, as adding an electron requires energy input to overcome electron-electron repulsion or disrupt stable configurations.

Statement B: "The process of removing an electron from an isolated gaseous atom is always endothermic." This is correct. Ionization energy is always positive (endothermic) because energy is always required to overcome the electrostatic attraction between the electron and the nucleus.

Step 2: Evaluate Statement C (First Ionization Energy Trend)○ Expand

Statement C: "The $1^{s t}$ ionization energy of boron is less than that of beryllium." This is correct. Beryllium (Be) has an electron configuration of $1 s^{2} 2 s^{2}$ , which is a stable, fully filled $s$ -orbital. Boron (B) has $1 s^{2} 2 s^{2} 2 p^{1}$ . Removing an electron from the $2 p^{1}$ orbital of boron is easier than removing an electron from the stable $2 s^{2}$ orbital of beryllium, due to the lower penetration and shielding effects on the $2 p$ electron. Thus, $I E_{1} (B) < I E_{1} (Be)$ . This is a known exception to the general trend of increasing ionization energy across a period.

Step 3: Evaluate Statements D and E (Electronegativity and Electropositivity)○ Expand

Statement D: "The electronegativity of C is 2.5 in $C H_{4}$ and $C C l_{4}$ ." This is incorrect. While the Pauling electronegativity of carbon is approximately 2.55, the *effective* electronegativity of an atom can vary depending on its chemical environment. Carbon in $C C l_{4}$ is bonded to highly electronegative chlorine atoms, making it more electron-deficient and thus having a different effective electronegativity compared to carbon in $C H_{4}$ (bonded to less electronegative hydrogen atoms).

Statement E: "Li is the most electropositive among elements of group I." This is incorrect. Electropositivity (metallic character) increases down a group due to increasing atomic size and decreasing ionization energy. Therefore, Lithium (Li) is the *least* electropositive element in Group 1; elements like Cesium (Cs) or Francium (Fr) are the most electropositive.

Based on the evaluation, only statements B and C are correct. Therefore, the correct option is 'B and C Only'.

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Chemistry Question 60 – JEE-MAIN 2025

Clue 1 of 3: Fundamental Definitions

🧠 Full Solution Path