Question

Chloride ion and potassium ion are isoelectronic. Then

• A. Their sizes are same
• B. Cl\(^{-}\) ion is bigger than K\(^+\) ion
• C. K\(^+\) ion is relatively bigger
• D. Their sizes depend on other cation and anion

Hint:

For isoelectronic species: Radius \(\propto \frac{1}{\text{Atomic Number (Z)}}\). The species with the highest number of protons will always be the smallest.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Isoelectronic species are atoms or ions that have the same number of electrons. For such species, the size is determined by the nuclear charge (number of protons). A higher nuclear charge pulls the same number of electrons closer to the center, making the ion smaller.
Step 2: Detailed Explanation:
1. Both $Cl^{-}$ and $K^{+}$ have 18 electrons.
2. Nuclear Charge (Protons): - $Cl$ has 17 protons. - $K$ has 19 protons.
3. Since $K^{+}$ has more protons (19) than $Cl^{-}$ (17), the nucleus of $K^{+}$ exerts a stronger attractive force on its 18 electrons.
4. This stronger attraction pulls the electron cloud inward, making $K^{+}$ smaller and $Cl^{-}$ relatively larger.
Step 3: Final Answer
$Cl^{-}$ ion is bigger than $K^{+}$ ion.