Answer:
200 Joules is the explosive energy in the inside the balloon. And that is
1 lb of TNT.
Explanation:

Volume of the balloon = V = 1 L = 
Pressure inside the balloon ,P= 200,000 Pa =
Explosive energy in the inside the balloon be E.
E = Pressure × Volume

1 lb of TNT = 
200 Joules =
1 lb of TNT
=
1 lb of TNT
I'm preatty sure it is in the periodic table xxx
In order to find the density of an object, you need to know the mass of the object and the volume.
That is why the unit of density is kg/m3.
Hope it helps