<span>When calcium hydroxide dissolves, it dissociates into
Ca(OH)2 = Ca2+ and 2OH-
Let's assign the variable X for the solubility of Ca2+ and OH
I.e Ca2+ = X and 2OH- = 2X
Then Ksp = [Ca2+][OH-]^2
So we have (X) (2X)^2 = 5.02 * 10^(-6)
4X^3 = 5.02 * 10 ^(-6)
X^3 = 5.02 * 10^(-6) / 4
X^3 = 0.003110
X = 0.1459</span>
Answer:
The temperature must be changed to 4 times of the initial temperature so as to keep the pressure and the volume the same.
Explanation:
Pressure in the container is P and volume is V.
Temperature of the helium gas molecules =
Molecules helium gas = x
Moles of helium has = 
PV = nRT (Ideal gas equation)
...[1]
After removal of helium gas only a fourth of the gas molecules remains and pressure in the container and volume should remain same.
Molecules of helium left after removal = 
Moles of helium has left after removal = 
...[2]




The temperature must be changed to 4 times of the initial temperature so as to keep the pressure and the volume the same.