Because when water is a solid the molecules are packed together,making it dense, but it expands because of how cold it is, almost in the same way like heat
If my memory serves me well, the right one is B. There is equal number of each type of atom on the reactant and product side. Check it, if I'm wrong.
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:
i think the answer is C ...