Answer:3.3
when you plug the [H+] you get..
-log(5x10^-4)
3.3
It can fit two more electrons within its valence shell to follow the octet rule. It will have a -2 charge to gain those two electrons to fill its octet.
Explanation:
Force applied on the gas will be as follows.

As, F = pressure × area. Hence, calculate the forces as follows.
= pressure × area
= 
=
N
= pressure × area
= 
=
N
-
=
N
Substituting the calculated values into the above formula as follows.

= (m + M) g
N =
N =
m = 472.76 kg
Thus, we can conclude that the mass is 472.76 kg.