4. To be considered acid rain, precipitation would have to

Precipitation is considered to be acidic when its pH falls below 5.6 (which is 25 times more acidic than pure distilled water).

Explanation:

I'm sorry if this does not help but I hope it does help.

is it multiple choice?

explanation:

the sun shines white and black light to our planet. the white light has all the colors in it. in our upper atmosphere, we have dust particles and oxygen molecules. the white light meaning all of the colors in a rainbow shines through the upper levels of the atmopshere and the blue light scatters across the entire planet. that is why our sky is blue.