Question

List atleast to conditions that could cause the pressure inside a sealed container of gas to increase

Answer 1

There are exactly three ways that could happen:

1).  The container was heated, and the gas inside it got warmer.

2).  Some part inside the container moved somehow, and made
      the inside volume smaller, so the gas got scrunched into a
      smaller space.

3).  Somebody pumped some more gas into the container, so
      a greater amount of gas had to live in the same space.