Questions

The inside of the bulb being a vacuum, the outside air rushes in when the bulb is broken. The vibrations of the rushing air molecules produce the sound.

GUI stands for Graphical User Interface.

A Graphical User Interface is a computer interface that allows users to interact with a device through graphical elements such as pictures and animations, as opposed to text-based commands.

From the hints,

Only two options for 1st and 2nd digits => 4,2 and 9,3 since it is single digits

Sum of second and third digit  = 10 

If 2 => 3rd digit = 8

If 3 => 3rd digit = 7

4th digit = 2nd digit + 1 => (2+1 =3) or (3+1 = 4)

Sum of all digits = 30

Let 5th digit be x

=> 1st possibility = 4 + 2 + 8 + 3 + x = 30 => x = 13 (Not possible since it has 2 digits)

=> 2nd possibility = 9 + 3 + 7 + 4 + x = 30 => x = 7

Therefore, the PIN is 93747