The pH scale is used to measure the acidity or alkalinity of a solution. It ranges from 0 to 14, with 7 being neutral. A solution with a pH lower than 7 is considered acidic, while a pH higher than 7 is alkaline or basic.

In this question, we are comparing a solution with pH = 2 to another solution with pH = 6. The pH scale is logarithmic, meaning that each whole number on the pH scale represents a tenfold difference in acidity or alkalinity.

To calculate the factor by which one solution is more acidic than another, we can subtract the lower pH from the higher pH and take the antilog of the result. In this case, subtracting 2 from 6 gives us 4. Taking the antilog of 4 gives us 10, which means that the solution with pH = 2 is 10 times more acidic than the solution with pH = 6.

Therefore, the correct answer is option 4: 10.