Which element is found in nature only in compounds? a. sodium b. helium c. oxygen d. nitrogen

18. use the activity series to predict whether the following synthesis reaction will occur. write the chemical equations for the reaction if it's predicted to occur. (s) + o2(g) -> *note: it is possible.*

The diagram shows the positions of the sun, moon and earth during spring tides, when the high tides are at their highest and low tides at their lowest. what is it about these positions that causes these high and low tides?

Helium decays to form lithium. which equation correctly describes this decay?