See image — GOC and Organic Chemistry Basics Chemistry Question

💡 Solution & Explanation

# Arranging in Decreasing Order of Acid Strength ## Option (a): $CH_4$, $NH_3$, $H_2O$, $HF$ **Step 1: Identify acid strength trends** - Acid strength increases with electronegativity of the atom bonded to hydrogen - Across a period (left to right), electronegativity increases: $C < N < O < F$ **Step 2: Compare the four compounds** - $CH_4$: Carbon is least electronegative → weakest acid (essentially non-acidic) - $NH_3$: Nitrogen more electronegative than C → very weak acid - $H_2O$: Oxygen more electronegative than N → weak acid, $K_a \approx 10^{-16}$ - $HF$: Fluorine most electronegative → strongest acid, $K_a \approx 10^{-3}$ **Step 3: Order by decreasing acid strength** $$HF > H_2O > NH_3 > CH_4$$ This matches option (a): **IV > III > II > I** ✓ **Why this is correct:** As electronegativity increases, the atom more strongly polarizes the O-H or N-H bond, making the hydrogen more acidic. Fluorine's high electronegativity makes HF significantly acidic, while the others are very weak acids.