Question

question ①
ph measures the concentration of ____________ in a solution.
answer
hydrogen atoms bonded to other atoms
any solute in a solution
free hydrogen ions
free hydroxide ions
i dont know yet

Explanation:

pH is defined as the negative logarithm of the concentration of free hydrogen ions ($H^+$) in a solution. It indicates the acidity or basicity of a solution.

Answer:

C. free hydrogen ions