4, 3, 1
Explanation:
Sb has four on the right, so it needs four on the left. It's all alone, so <u>4</u>.
O2 comes in pairs, so you only need <u>3</u> of those to get six oxygens.
And 1 is the place holder for the right side since we got the left to match perfectly.
Answer: The correct option is A.
Explanation: In a chemical reaction, reactants react to form a number of products.
For the formation of products, the bonds of the individual reactants must be broken and the bonds of the products must be formed.
For example: Formation of water from hydrogen gas and oxygen gas. Reaction follows:

The Bonds of hydrogen and oxygen molecule are broken and new bonds between hydrogen and oxygen atoms are formed to give water molecule.
Of which reaction may I ask? And do you mean 1-bromo-2-methylcyclohexane??
Explanation:
It is known that 1 gram contains 1000 milligrams. And, mathematically we can represent it as follows.
or 
So, when we have to convert grams into milligrams then we simply multiply the digit with 1000. And, if we have to convert a digit from milligrams to grams then we simply divide it by 1000.