Choice 2 possibly, not positive
Answer:
each of two or more forms of the same element that contain equal numbers of protons but different numbers of neutrons in their nuclei, and hence differ in relative atomic mass but not in chemical properties; in particular, a radioactive form of an element.
Explanation:
Answer:
, 0.533 L
Explanation:
According to the law of conservation of mass, mass can neither be created nor be destroyed. Thus the mass of products has to be equal to the mass of reactants. The number of atoms of each element has to be same on reactant and product side. Thus chemical equations are balanced.

According to avogadro's law, 1 mole of every substance occupies 22.4 L of volume at STP.
Number of moles =
moles of calcium carbonate = 
As 1 mole of calcium carbonate produces = 22.4 L of carbon dioxide at STP
Thus 0.0238 moles of calcium carbonate produces =
of carbon dioxide at STP
That would be the NOBLE GASES (Helium, Neon, Argon, Krypton, Xenon, Radon). Because these elements have a filled outer shell (thus giving them the full octet that other elements crave), they are stable elements under normal circumstances and as such resist chemical combination.
Plz note that under special conditions, noble gases such as Xenon and Radon can form compounds (Xenon Fluoride and Oxide; Radon Fluoride)