Scientists divide time into four main sections. two sections are the precambrian and the paleozoic. what are the other two sections?

a.
triassic and cenozoic

b.
pennsylvanian and mesozoic

c.
ice age and precambrian

d.
cenozoic and mesozoic

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

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How can nonpolar molecule contain polar covalent bonds