Hidrogen gas is a diatomic gas, this is H2, which means that one molecule of gas has two atoms (every molecule of hydrogen gas consists in H2). The particles in gases are the molecules, not atoms. So, every molecule is a particle, and when you are told that you have 1 mole of hygrogen gas means that you have 1 mole of H2 molecules which is the same that 1 mole of particles. Therefore, the answer is one mole.
The number of particles in 1 mole of hydrogen gas is ________.