An extensive property is a property that depends on the amount of matter in a sample. The mass of an object is a measure of the amount of matter that an object contains.
In chemistry and related fields, a property is a characteristic of a substance or element. In the case of extensive properties, these are properties that vary with the amount of the substance or the amount of matter. Mass is classified as an extensive property because this refers to the amount of matter, which increases or decreases with the amount of a substance. Moreover, extensive properties differ from intensive properties because intensive properties do not depend on the quantity of mass or material. Thus, the mass of a material is an extensive property.
I think it is true. The formation reaction always means that the product substance is made directly and all by the elements of the reactants. And standard means under 25℃ and one atmosphere.
