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.
Choose the correct answer from the options given below:
Options
Solution
Sol. [Key Concept: p-block statements — Ga melting point, electronegativity, isoelectronic species, ionisation enthalpy]
Both Ga and Cs have low melting points.
| Element | Melting point/K |
|---|---|
| Ga | 303 |
| Cs | 302 |
On Pauling scale, the electronegativity value of N and Cl have same (3.0).
$Ar,K^{+},{Cl}^{-},{Ca}^{2 +}$ and $S^{2 -}$ have 18 electrons. So these are isoelectronic species.
The correct order of first ionization enthalpy is $Si > Mg > Al > Na$
First ionization enthalpy of Mg is higher than Al because the penetration of a 3s-electron to the nucleus is more than that of a $2p$-electron.
Generally, down the group atomic radii increases
| Atom | Atomic radius/pm |
|---|---|
| Li | 152 |
| Rb | 244 |
| Li | 262 |
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