Achange in color, such as rusting of metal, is a sign
a.) a chemcal change is taking place.
b.) a physical change has just taken place.
c.) oxygen is present
d.) organic chemicals are present

A change in colour such as rusting of metal is a sign that a chemical change is taking place on the surface of the metal.

Option A

Explanation:

Rusting is the product of chemical reaction occurring on the surface of any metals when it comes in contact with elements like oxygen, water or other oxidising agents.

These oxidising agents remove the electrons from the surface on which they are reacting and form a layer of precipitate as a product of the oxidation reaction, thus changing the colour of the substance.

Any reaction where a new substance formed is termed as chemical change or chemical reaction occurring on the metal. So in this case also, the change in colour of the metal is a sign of chemical change.

s too much pool water may lead to chlorine poisoning. the concentration of chlorine in public drinking water is extremely low and not harmful to human health. sooo yeahh

explanation:

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 !