Question

Which of the following statements are true?
A. Unlike Ga that has a very high melting point, Cs has a very low melting point.
B. On Pauling scale, the electronegativity values of N and C are not the same.
C. $Ar, K^{+}, Cl^{–}, Ca^{2+} and S^{2–}$ are all isoelectronic species.
D. The correct order of the first ionization enthalpies of Na, Mg, Al, and Si is Si $>$ Al $>$ Mg $>$ Na.
E. The atomic radius of Cs is greater than that of Li and Rb.
Choose the correct answer from the options given below:

• A. C and E only
• B. C and D only
• C. A, C, and E only
• D. A, B, and E only

Hint:

Isoelectronic species have the same number of electrons, but not necessarily the same number of protons. Always check the electron configurations and atomic sizes carefully when analyzing such questions.

Answer 1

The Correct Option is C

Evaluating each statement:

- Statement A: Cs possesses a significantly lower melting point than Ga. This is true. As an alkali metal, Cs exhibits a much lower melting point compared to Ga.

- Statement B: Nitrogen (N) and Carbon (C) exhibit different electronegativity values on the Pauling scale. N has an electronegativity of 3.04, while C has 2.55, making N more electronegative. This statement is true.

- Statement C: Ar, K\textsuperscript{+}, Cl\textsuperscript{–}, Ca\textsuperscript{2+}, and S\textsuperscript{2–} share the same electron configuration with 18 electrons, classifying them as isoelectronic species. This statement is true.

- Statement D: The assertion that the first ionization enthalpies are ordered as Si>Al>Mg>Na is false. This is incorrect because Mg has a higher ionization enthalpy than Al. The correct order is Si>Mg>Al>Na.

- Statement E: The atomic radius of Cs (cesium) exceeds that of Li (lithium) and Rb (rubidium). This is true, consistent with the trend of increasing atomic size down a group in the periodic table.


Consequently, the correct answer is (3) A, C, and E only.