When the pressure on the surface of a gas is increased, the inter-particle forces between the gas particles will increase.

Explanation:
Gas particles are in constant motion and have a significant amount of space between them. The pressure of a gas is a measure of the force exerted by the gas particles on the walls of the container per unit area.

Increase in pressure:
When the pressure on the surface of a gas is increased, it means that the force exerted by the gas particles on the walls of the container has also increased. This increase in force implies that the gas particles are colliding with the walls of the container more frequently and with greater energy.

Impact on inter-particle forces:
The inter-particle forces in a gas are generally very weak compared to the inter-particle forces in liquids or solids. In a gas, the particles are not strongly attracted to each other and are relatively far apart. However, when the pressure is increased, the gas particles are forced closer together, resulting in a higher frequency of collisions and a greater number of forceful collisions.

Increase in inter-particle forces:
As the gas particles collide more frequently and with greater energy, the inter-particle forces between them will increase. This increase in inter-particle forces is a direct result of the increased pressure on the gas. The gas particles will experience stronger interactions with each other, leading to a slight decrease in the overall volume of the gas.

Conclusion:
Therefore, when the pressure on the surface of a gas is increased, the inter-particle forces between the gas particles will increase. This is because the increased pressure causes the gas particles to collide more frequently and with greater energy, resulting in stronger interactions between them.