What is the percentage of water by mass in CoCl2 × 2H2O? ​

What happened to the amount of carbon dioxide in the atmosphere from 2010–2017?

Which of the following is an example of physical change not a chemical change? a) a log gives off heat and light as it burns. b) a tree stores energy from the sun in its fruit. c) a penny lost in the grass slowly changes color. d) a water pipe freezes and cracks on a cold night.

In which reaction is precipitation occurring?