Question

Correct order of Acidic strength is :
1. CH₄ > NH₃ > H₂O > HF
2. HF > H₂O > CH₄ > NH₃
3. CH₄ < NH₃ < H₂O < HF
4. HF > CH₄ > H₂O > NH₃

Answer 1

Correct Answer - Option 3 : CH₄ < NH₃ < H₂O < HF

Explanation:

• Consider the given compounds CH4, NH3, H2O and  HF . These all are hydrides of first row elements in the periodic table.
• When we compare the compounds in the same horizontal row of the periodic table, the dominant factor becomes the electronegativity of the atom bond to the hydrogen.
• It is because the electron density is shifted towards the highly electronegative element, which facilitates the release of the H⁺ ion. 
• We know that the electronegativity increases across a row in the periodic table from left to right. 
• Here, the relative electronegativities is in the order C < N < O < F 
• Because fluorine is the most electronegative element, the bond H-F is more polarized, and the proton in HF is the most positive. So, H-F is most acidic. 

The increasing order of acidic strength of the given hydrides are given by CH4 < NH3 < H2O < HF