Question

Number of bonding pairs (X) and lone pairs (Y) around the central atom in the \(I_3^-\) ion is

• A. \(X-2,\;Y-2\)
• B. \(X-2,\;Y-3\)
• C. \(X-3,\;Y-2\)
• D. \(X-4,\;Y-3\)

Hint:

In \(AX_2E_3\) type species (like \(I_3^-\)):
Electron geometry is trigonal bipyramidal
Molecular shape is linear

Answer 1

The Correct Option is B

Step 1: Consider the triiodide ion \(I_3^-\). The central iodine atom is bonded to two iodine atoms.
Step 2: Valence electrons: \[ \text{Iodine} = 7,\quad \text{Extra charge} = 1 \] \[ \text{Total electrons on central I} = 8 \]
Step 3: Two iodine–iodine bonds are formed with the central atom, giving: \[ \text{Bonding pairs (X)} = 2 \]
Step 4: Remaining electrons form lone pairs on the central atom: \[ \text{Lone pairs (Y)} = 3 \]
Step 5: Thus, the central iodine atom has: \[ \boxed{2\ \text{bonding pairs and}\ 3\ \text{lone pairs}} \]