Asample of a gas is placed inside a cylinder that is a fixed size. the cylinder is heated as additional gas is added to it. what will most likely happen to the pressure of the gas inside the cylinder?

The pressure will increase.

Explanation:

The gas state has the ability by the distance of their particles, to compress or expand, in this case, the cylinder can support certain quantity of gas inside it.

But when more quantity of gas is added, the particles will increase, in this way, the energy at which they move will increase by the number of particles present, so the heat increases.

Also, since inside there is a lot of particles moving, the pressure that they exhort is bigger.