Potential energy stored in a spring => kinetic energy of a toy
The answer to this is 22, confirmed by gradpoint
Bromine (Br) is the only element listed that is a diatomic element. I believe that Bromine is going to be your answer.
The volume did not change, it remained at 20 ml
<h3>Further explanation</h3>
Given
20 ml a sample gas at STP(273 K, 1 atm)
T₂=546 K
P₂=2 atm
Required
The volume
Solution
Combined gas Law :

Input the value :

The volume does not change because the pressure and temperature are increased by the same ratio as the initial conditions (to 2x)