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

Let’s evaluate each statement:
- Statement A: Cs has a very low melting point compared to Ga. This statement is true, as cesium (Cs) is an alkali metal and has a much lower melting point compared to gallium (Ga).
- Statement B: On the Pauling scale, the electronegativity values of N and C are actually different. Nitrogen (N) has a higher electronegativity (3.04) than carbon (C) (2.55). This statement is true.
- Statement C: Ar, K\textsuperscript{+}, Cl\textsuperscript{–}, Ca\textsuperscript{2+}, and S\textsuperscript{2–} all have the same electron configuration (18 electrons), so they are isoelectronic species. This statement is true.
- Statement D: The correct order of the first ionization enthalpies is Si>Al>Mg>Na. This is incorrect because magnesium (Mg) has a higher ionization enthalpy than aluminum (Al). The correct order should be Si>Mg>Al>Na.
Thus, this statement is false.
- Statement E: The atomic radius of Cs (cesium) is greater than that of Li (lithium) and Rb (rubidium). This statement is true, as atomic size increases down the group in the periodic table.

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