1) The metal which reduces the other compound is the one higher in the reactivity. So in this case it is
.
2) The substance which brings about reduction while itself getting oxidised (that is losing electrons) is called a reducing agent. Here, $\mathrm{Zn}$ is the reducing agent and reduces Cobalt Oxide to Cobalt while itself getting oxidised to Zinc oxide.
Answer:
sound waves travel.faster through materials that are more dense
Never mind, I did the problem wrong, I deeply apologize.
A chemical reaction does happen between sodium and water to form Sodium Hydroxide (NaOH) and Hydrogen Gas (H-2)