How many half-lives have passed when there are 3 times as much daughter isotope as parent isotope?

2 half lives.

Explanation:

Suppose there are 100g of parent isotope at the start.

After 1 half-life  there will be 50g of parent and 50g of daughter isotope.

After another half life there is  25 g of parent and 75g of daughter isotope.

answer:

the reaction is type of combination reaction.

explanation:

on the product side, there are 2 molecules of bonded to fe   which means one atom of fe are combined two molecules of . so, balanced chemical equation becomes :

this reaction follows the reaction type of combination reaction. a combination reaction is defined as chemical reaction in which reactants combines together to form a single product.