When an iron nail is ground into powder, its mass . a. stays the same
b. decreases
c. increases
d. cannot be determined

When paper turns yellow-brown upon exposure to sunlight, what type of change is likely taking place?

a. a physical change
b. a chemical change
c. neither a physical change nor a chemical change
d. both a physical change and a chemical change

1) The mass of any substance remains the same irrespective of the state.

Thus, an iron nail ground into powder should have the same mass unless parts of it got lost during grinding.

2) A paper that turns yellow-brown upon exposure to sunlight is likely undergoing a chemical change. It could be that the light oxidizes the atoms of the paper.

Chemical changes occur when the atoms of a substance combine with another substance to form new products. New products are not formed in physical changes and the original product can be retrieved by physical means.

More on physical and chemical changes can be found here: link

Explanation:

(a) The mass of an object remains the same always. It is independent of its location. In this case, an iron nail is ground into powder. It means that its mass will remain unchanged. Hence, (a) is the correct option.

(b) Whenever there is a change of color of an object, a chemical reaction occurs. It shows that a reaction happens there. In this problem, a paper turns yellow-brown upon exposure to sunlight. A chemical reaction takes place there. Hence, (b) is the correct option.

1. for the first question, we must find the mass of the anhydrous salt, mgso₄. the molar mass for mgso₄·7h₂o is 246.47 g/mol, while that of mgso₄ is 120.37 g/mol.7.834 g mgso₄·7h₂o * 1 mol mgso₄·7h₂o/246.47 g * 1 mol mgso₄/1 mol mgso₄·7h₂o * 20.37 g mgso₄/mol = 0.647 g mgso₄

2. mass of water = mass of sample - mass of anhydrous salemass of water = 7.834 - 0.647 = 7.19 gpercent water in hydrate = 7.19/7.834 * 100 = 91.74%