First of all, as you seen the gases are noble which means that will not react with each other and in this case each gas create individual pressure.
P= total pressure
P = pressure of neon
P = pressure of argon
P = pressure of helium {which is required}
P = P
+ P
+ P
1.25 = 0.68 + 0.35 + P
P = 1.25 - [0.68 + 0.35] = 0.22 atm
I looked on a solubility chart to answer this question, and hydroxides are generally insoluble (with some exceptions of course). However, it says to consider as an insoluble substance, though it may be moderately soluble.
The answer that you are most likely looking for is: Yes, a precipitate does form - this is due to the double placement reaction:
+
→
+