Answer: The correct answer is Option B.
Step-by-step explanation:
Rust is a reddish-brown substance which is formed by the oxidation of iron in the presence of moisture. The chemical formula for rust is

Law of conservation of mass states that mass can neither be created nor be destroyed but it can only be transformed from one form to another form.
This also means that total mass on the reactant side must be equal to the total mass on the product side.
The chemical equation for the formation of rust follows:

We are given:
Mass of
= x
Mass of
= 10 kg
Total mass on reactant side = x
Total mass on product side = 10 kg
So, by applying law of conservation of mass, we get:

Hence, the correct answer is Option B.