Here's how to determine the number of valence electrons in acetic acid (CH3CO2H):

1. Valence Electrons per Atom:

* Carbon (C): 4 valence electrons

* Hydrogen (H): 1 valence electron

* Oxygen (O): 6 valence electrons

2. Total Valence Electrons:

* Carbon: 2 carbons * 4 valence electrons/carbon = 8 valence electrons

* Hydrogen: 4 hydrogens * 1 valence electron/hydrogen = 4 valence electrons

* Oxygen: 2 oxygens * 6 valence electrons/oxygen = 12 valence electrons

3. Total: 8 + 4 + 12 = 24 valence electrons

Therefore, there are 24 valence electrons in the acetic acid molecule (CH3CO2H).