Which of the following is a true statement? a. Periods form horizontal rows; groups form vertical columns
b. Groups form horizontal rows; periods form vertical columns
c. Categories form horizontal rows; gases form vertical columns
d. Gases form horizontal rows; categories form vertical columns

a. Periods form horizontal rows; groups form vertical columns

Explanation:

On the periodic table of elements, it is true that periods form horizontal rows and groups form vertical columns.

In the periodic table, elements having the same number of electrons in the outermost shell of their atoms are placed over one another in vertical columns.

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.