Question

testing for ph levels can be useful in a variety of ways. healthcare professionals may use ph tests on saliva or urine samples to help diagnose disorders. ph tests are also performed in the home on water samples from, for example, swimming pools. 3. ph strips measure the number of select in a solution.

Explanation:

The pH of a solution is related to the concentration of hydrogen ions ($H^+$). pH strips work by measuring the hydrogen - ion concentration in a solution.

Answer:

Hydrogen ions ($H^+$)