16. Which of the following substances are elements (check all that apply)? hydrogen
carbon dioxide
calcium
water
air

What are the most explosive events that occur on the sun? umbras solar flares solar winds prominences

'which of these statements about the scientific method is not true? all experiments must follow the same number of steps in the procedure. experiments may be repeated several times. some unexpected results can be beneficial. experimental results may or may not support the hypothesis.

Explain the source of radioactivity in uranium in earth’s crust by which it produces nuclear radiation