The number of bonds for a neutral atom is equal to the number of electrons in the full valence shell (2 or 8 electrons) minus the number of valence electrons. This method works because each covalent bond that an atom forms adds another electron to an atoms valence shell without changing its charge.
The pond weeds are the producers because they are a plant
The correct answer is
D burning wood
because it's changing the wood.
The other's are physical changes because it's still the same thing, it's just in a different form.
Glad I could help, and good luck!
AnonymousGiantsFan