The word preparing has three syllables. It is divided as pre-par-ing.
When dividing words into syllables, each part usually contains a single vowel sound. For preparing, the division follows the natural breaks of pronunciation and vowel sounds:
pre / par / ing
“Preparing” is pronounced with emphasis on the second syllable, which sounds like “pair.”
The phonetic representation is often written as /pri-PAIR-ing/.
Author’s summary: The word “preparing” contains three syllables, divided as pre-par-ing, with stress on the middle part.