(c) the color turns deep dark and then at certain level, it turns back to light green.
(d)fastest.
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)}}$
False, in an exothermic reaction, an increase in temperature does not favor the formation of products. Instead, it favors the backward reaction. An exothermic reaction is a reaction where energy is transferred from the system out to the environment.
I think the answer is research and development.