Answer:
I think that it it correctly balanced that is my opinion and, because the way it is set up, that the answer will tell you weather or not it is correctly balanced or not.
Answer: The pressure will be 18.05 atm.
Explanation: Expression for ideal gas equation is :
where,
P = Pressure of the gas = ? atm
V = Volume of the gas = 0.333L
n = Number of moles of gas = 0.250 moles
R = Universal gas constant = 
T = temperature of the gas = 20°C = (273 + 20)K = 293K
Putting values in above equation, we get:
P = 18.05 atm
A3B2
bond is ionic
A is in group 2 (you can pick any like Ca)
B is in group 5 (like B)
the other question:
the reason is they are neutral gas and they already have 8 electrons except for He which is 2 and are completely stable so don't want to loose any electron vs Li and Na which have only 1 electron in the outer layer and are willing to loose that one to become stable.
