Answer: Mg is the excess reactant for the forward reaction.
Explanation: It is a stoichiometry problem and solved with the help of given grams and using balanced equation. Grams of both the reactants are converted to moles and divided by their coefficients. The excess reactant is the one for which we get the highest number on doing above steps.
The balanced equation is:

Molar mass of silicon tetra chloride is 169.9 gram per mol and the molar mass of Mg is 24.3 gram per mol.

= 

= 2.67 mol Mg
From balanced equation, the coefficient of silicon tetra chloride is 1 and that of Mg is 2. So, we will divide the moles of silicon tetra chloride by 1 and that of Mg by 2 and see which one gives highest number.
For silicon tetra chloride,
= 0.317
and for Mg,
= 1.34
The highest number is for Mg and so the excess reactant for the forward reaction is Mg.
When we talk about the gram weight of any food item, it may or may not include the gram weight of its different nutrient molecules. It may have different reasons to it. One of the reasons can be because the nutrient molecule might contain a large percentage or proportion of water. Also, the nutrient molecules might be insoluble or indigestible fiber so it does not add up to the total gram weight of food.
Answer:
5.21
Explanation: You can only have 3 digits, so you would round to the hundredths place
Rust is an iron oxide and formed by the reaction of iron and oxygen in the presence of moisture. So the answer would be C