2025 Classification of Elements and Periodicity in PropertiesPeriodic Trends in Properties of Elements Medium Question 5 of 41 in Classification of Elements and Periodicity in Properties

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

The answer is B.

Solution

C and E are true. Ga also has a very low melting point ($29.8^\circ\text{C}$); N and Cl both have electronegativity $3.0$ on Pauling scale; IE1 order is $\text{Si} > \text{Mg} > \text{Al} > \text{Na}$.

Statement A is false because both Ga ($29.8^\circ\text{C}$) and Cs ($28.5^\circ\text{C}$) have very low melting points. Statement B is false because both N and Cl have identical electronegativity of 3.0 on Pauling's scale. Statement C is true as all contain 18 electrons. Statement D is false because the actual order is $\text{Si} > \text{Mg} > \text{Al} > \text{Na}$ (due to stable filled $3s^2$ in Mg). Statement E is true as atomic radius increases down Group 1: $\text{Cs} > \text{Rb} > \text{Li}$. Hence only C and E are true.

Concept Periodic Trends and Isoelectronic Species

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41 questions from this chapter have appeared across 23 exam years.