The adjustment that would increase the speed of the 300 light particles is keeping the pressure constant and increasing the temperature.
Temperature is defined as the average kinetic energy of the molecules of a substance. The molecules of a substance are the particles referred to here.
When the temperature of a substance is increased, the speed of the particles in the container increases accordingly.
Hence, for the 300 light particles in an airtight container, the increase in the speed of the particles is achieved by keeping the pressure constant and increasing the temperature .
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