I believe that the chemical formula for an acid often begins with H, which means C is your answer.
a) The change here is that metallic iron is converted into ions and copper is deposited. This is called a displacement reaction.
b)
is oxidised in this reaction.
c)$ \mathrm{Fe_{(s)}+ CuSO_{4(aq)} \rightarrow FeSO_{4(aq)} + Cu_{(s)}}$
B) Humus is the decayed organic material that gives soil its dark brown or black color.
Explanation:
The Bohr hypothesis shows that an atom has an circular orbit of electrons outside the nucleus in a revolving orbit. In Bohr model for Nitrogen there are two orbits s and p. The s has two electron and p has five. Whereas in Bohr neon model there are also orbital s, and p.. The s orbital has 2 electron and the p orbital has 8 electron in it.