Question

ph is a measure of or (how basic something is).
acidity alkalinity

Explanation:

Identify the blanks and options

The sentence is: "pH is a measure of [Blank 1] or [Blank 2] (how basic something is)."
The available draggable options are "acidity" and "alkalinity".

Match options to context

"Alkalinity" is directly synonymous with "how basic something is", which is placed in parentheses right after the second blank.
Therefore, the first blank refers to "acidity" and the second blank refers to "alkalinity".

Answer:

pH is a measure of <blank>acidity</blank> or <blank>alkalinity</blank> (how basic something is).