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…

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 Cl 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.

1. A. A, B, and E only
2. B. C and E only (Correct answer)
3. C. C and D only
4. D. A, C, and E only

Correct Answer

Option B — C and E only

Detailed Solution & Explanation

The correct answer is C and E only.

Key Points

• (A) is false: both Ga (m.p. 303 K) and Cs (m.p. 302 K) have low melting points, so the contrast stated is wrong.
• (B) is false: on the Pauling scale both N and Cl have electronegativity $=3.0$ (they are the same).
• (C) is true: Ar, K$^+$, Cl$^-$, Ca$^{2+}$ and S$^{2-}$ each have 18 electrons — isoelectronic.
• (D) is false: the correct order is Si > Mg > Al > Na (Mg has higher first IE than Al due to its stable filled 3s$^2$).
• (E) is true: atomic radius increases down the group (Li 152 pm < Rb 244 pm < Cs 262 pm).