"How many hydrogen atoms does it take to reach the Moon?"

One.

How many hydrogen atoms does it take to reach the Moon if there are in single file?

"In the Bohr model of the structure of an atom, put forward by Niels Bohr in 1913, electrons orbit a central nucleus. The model says that the electrons orbit only at certain distances from the nucleus, depending on their energy. In the simplest atom, hydrogen, a single electron orbits, and the smallest possible orbit for the electron, that with the lowest energy, is most likely to be found at a distance from the nucleus called the Bohr radius.

According to 2006 CODATA the Bohr radius of hydrogen has a value of 5.2917720859(36)×10−11 m "
http://en.wikipedia.org/wiki/Bohr_radius

So if you want to line up a hydrogen atom in single file at a bohr radius, you have about 5.29177 x 10^11 per meter.

Lecture 25. Bose-Einstein Condensation:
"At this density, the distance between the atoms is ~ 10^4 times greater than the Bohr radius, and the interatomic interactions are extremely weak. The condensation is driven by statistics rather than by interactions! "

"The challenge when producing a Bose condensate is to cool a gas such that the average distance between the atoms becomes very small without the atoms forming molecules or the gas changing into a liquid."
...
While the Boulder and MIT groups led the way in exploring the properties of condensates, other groups achieved BEC with hydrogen, helium-4, rubidium-85 and potassium-41."
http://physicsworld.com/cws/article/print/3433

So atomic hydrogen at distance of 10^4 greater than Bohr radius would be 5.2917720859(36)×10−7 m
Or about 5.29177 x 10^7 per meter

The average distance to the Moon is 384,400 km from Earth
Or 3.844 x 10^8 meters

So: about 2 x 10^16 hydrogen atoms in a Bose condensate
state in single file could reach the average distance to the Moon.

If you wanted to use molecular hydrogen it could a be gas, liquid, or solid. One also use hydrogen in plasma state.