Why is the organization of the periodic table by physical properties not very useful?

It shows no regular pattern

Explanation:

Physical properties of an element are those we can observe and feel with our senses. Also, the use special equipment can enhance our perception of these properties.

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.

your answer is a. the enthalpy of formation for a pure element in its standard state is always positive.