Which is true of ultraviolet rays?
they your body produce vitamin d.
they are visible to the naked eye.
they provide the energy that makes your morning toast.
they carry information to televisions and radios.

Dumbledore decides to gives a surprise demonstration. he starts with a hydrate of na2co3 which has a mass of 4.31 g before heating. after he heats it he finds the mass of the anhydrous compound is found to be 3.22 g. he asks everyone in class to determine the integer x in the hydrate: na2co3·xh2o; you should do this also. round your answer to the nearest integ