Which of these is NOT found in the earths crust?

Oxygen
Iron
Sulphur
Helium​

Which of these conditions most likely produces an unstable isotope?

Phosphorous acid, h3po3(aq) , is a diprotic oxyacid that is an important compound in industry and agriculture. p k a1 p k a2 1.30 6.70 calculate the ph for each of the points in the titration of 50.0 ml of 1.5 m h3po3(aq) 1.5 m h 3 po 3 ( aq ) with 1.5 m koh(aq). 1.5 m koh ( aq ) .

Need what is special about water as a compound? how does water regulate climate? what drives water evaporation?   why is the water vapor fresh water when it rises from the ocean? why might freshwater in the form of snow take longer to enter the water cycle again than liquid precipitation?   what is an aquifer? what role do people play in the water cycle? plz just answer as many as you can ! thx if you !