Asolution

a- has a uniform composition and is able to be separated by physical means.

b- has a heterogeneous composition and is able to be separated by physical means.

c- has a heterogeneous composition and is able to be separated by chemical means.

d- has a uniform composition and is only able to be separated by chemical means.

what is the volume occupied by 40 grams of argon gas (ar) at standard conditions? what volume, in liters, is occupied by 1.5 x 1023 

2fe + 3h2so4 -> fe2(so4)3 + 3h2

it is necessary to balance equations in order to get the proper amount of reactants as well as products in order not to make a miscalculation.

you cannot change the subscripts as that would change the substance itself. for instance, diatomic elements such as h2 only have the subscript two when a gas. another example would be so4, if you were to change the subscript, the element would no longer be sulfate.

we change the coefficients instead as that only changes the number of molecules rather than the substance itself.

hope this !