The answer is C.
example: 3NaCl + Al ----> AlCl₃ + 3Na
2 hydrogen and 2 chlorine on the reactant side(left of the arrow)
There is only 1 H and 1Cl on the products side so the balanced equation would be;
H2 + Cl2 —> 2 HCl
Among the choices, the polyatomic ion is only the third choice, NH4+ where it is composed of nitrogen one atom of nitrogen and 4 atoms of hydrogen. Choice 2 is a monoatomic atom being composed only of calcium. Then, the first and fourth choices are not ions because they are not charged.
Hair is dead skin cells that pile on top of each other to "grow".
Opposites attract, like for example magnets, one is positive and the other is negatively charged, they will attract
