Hg + O2 --> HgO + O
Note that Mercury has a variable valency.
Because if they are not balanced, then the amount of reaction is not equal to the amount of the product. You must have the same ratio of atoms on both sides of the equation because we are not losing moles of each element.
Antimony has two naturally occurring isotopes. Their abundance is given in the pic attached below
C. Lowering the temperature
At the lower temperature, particles have less kinetic energy, so they move slower.
A i belive is the correct answer
