Here's how to determine the number of valence electrons in serine:

1. Identify the atoms in serine:

Serine's chemical formula is C3H7NO3. This means it contains:

* 3 carbon atoms (C)

* 7 hydrogen atoms (H)

* 1 nitrogen atom (N)

* 3 oxygen atoms (O)

2. Determine the valence electrons of each atom:

* Carbon (C): 4 valence electrons

* Hydrogen (H): 1 valence electron

* Nitrogen (N): 5 valence electrons

* Oxygen (O): 6 valence electrons

3. Calculate the total valence electrons:

* Carbon: 3 atoms * 4 valence electrons/atom = 12 electrons

* Hydrogen: 7 atoms * 1 valence electron/atom = 7 electrons

* Nitrogen: 1 atom * 5 valence electrons/atom = 5 electrons

* Oxygen: 3 atoms * 6 valence electrons/atom = 18 electrons

Total valence electrons in serine: 12 + 7 + 5 + 18 = 42 electrons

Therefore, serine has 42 valence electrons.