The correct decreasing order for acid strength is :

The one that is extensively used as a piezoelectric material is :

Arrange the following amines in the decreasing order of basicity :

20 mL of 0.1 M H₂SO₄ solution is added to 30 mL of of 0.2 M NH₄OH solution. The pH of the resultant mixture is : [pk_b of NH₄OH = 4.7].