Solveeit Logo
Login

Question

Question: Select the correct sequence of increasing radius (left to right)...

Select the correct sequence of increasing radius (left to right)

A

Se2−^{2-}, O2−^{2-}, F−^{-}

B

Ca2+^{2+}, Ar, K+^{+}

C

Se, As, Ge

D

Fe, Fe2+^{2+}, Fe

Answer

Se, As, Ge

Explanation

Solution

  • (A) Se2−^{2-}, O2−^{2-}, F−^{-}: O2−^{2-} and F−^{-} are isoelectronic species. O2−^{2-} (Z=8) has a lower nuclear charge than F−^{-} (Z=9), so O2−^{2-} is larger than F−^{-}. Se2−^{2-} is in Period 4, while O2−^{2-} and F−^{-} are in Period 2. Radii increase down a group, so Se2−^{2-} is larger than O2−^{2-} and F−^{-}. The correct order is F−^{-} < O2−^{2-} < Se2−^{2-}. Option (A) is incorrect.
  • (B) Ca2+^{2+}, Ar, K+^{+}: These are isoelectronic species with 18 electrons. Ca2+^{2+} (Z=20), K+^{+} (Z=19), Ar (Z=18). Radius decreases with increasing nuclear charge. The correct order of increasing radius is Ca2+^{2+} < K+^{+} < Ar. Option (B) is incorrect.
  • (C) Se, As, Ge: These elements are in Period 4. Ge (Group 14), As (Group 15), Se (Group 16). Atomic radius generally decreases across a period from left to right. Thus, Radius(Ge) > Radius(As) > Radius(Se). The correct sequence of increasing radius is Se, As, Ge. Option (C) is correct.
  • (D) Fe, Fe2+^{2+}, Fe: A cation is smaller than its parent atom. Fe2+^{2+} is smaller than Fe. The sequence Fe, Fe2+^{2+}, Fe is incorrect because Radius(Fe) > Radius(Fe2+^{2+}).