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, and S 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
A, B and E only
- B
C and E only
- C
C and D only
- D
A, C and E only
C is correct: Ar, K, Cl, Ca, S all have 18 electrons, hence isoelectronic.
E is correct: down Group 1, atomic radius increases (Li < Na < K < Rb < Cs), so Cs > Rb > Li.
A is wrong: both Ga and Cs have low melting points (Ga melts near body temperature; Cs near 28 °C).
B is wrong: N and Cl have nearly the same Pauling electronegativity (≈ 3.0).
D is wrong: the actual order has anomalies — Mg > Al because removing an electron from Al breaks a filled 3s; Si > Al but Al < Mg.
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