PH stands for "Potential Hydrogen" and the PH scale ranges from 0-14. PH refers to the ability to attract hydrogen ions.
The PH of a solution either indicates acidity of the solution or alkalinity of the solution. A solution which has PH 7 above is a base solution where a solution with PH less than 7 is an acidic solution.
Pressure on the inside of the balloon was greater than the pressure on the outside of the balloon so it pushed out until the pressures equalized.