<span>Decomposition reaction.</span>
A) Ca(OH)2 + CO2 —> CaCO3 + H2O
B) when Ca(OH)2 is reacted with CO2, the CaCO3 produced is a precipitate which turns the solution milky
D because Carbon and Oxygen form covalent compounds. I wasn't the greatest at chem., but I'm pretty sure this is correct :D let me know if I gave you the right answer.
The helium would expand into the air of the room. Depending on how big the room is, and the amount of helium in the jar, it could cause damage to health. The only way this would happen is if the room was small and the jar was big.
I hope this helps!