Which number represents an acidic ph, 4 or 9?

The calculation of pH is based on the activity (aH) of hydrogen ions (H+) dissolved in solution. Specifically, the pH range of numbers is based on a logarithmic scale:

pH=-log (aH)

Log functions are used to rescale very large numbers (or very small numbers) into values much closer to 1. This is often done to deal with more reasonable
Numbers (for pH, 1 to 14). Mathematically, the negative sign in the formula means that pH must be less than 1.

The lower the number on the pH scale, the greater the concentration of hydrogen ions and the greater the material's acidity. The higher the number assigned on the pH scale, the greater the concentration of hydroxide ions and the more basic, or alkaline, the material.

The answer is 4.

Idon't see the pic?

The correct answer is c. orbital shape. "the angular momentum quantum number l describes the shape of an orbital. it corresponds to each orbital type, i.e. (0,1,2,−1)=(s,p,d,f,g,"