I didn't know that. Thanks!

Also:

    Second, thermal radiation, as usually defined, also disappears.
    There is no longer any air for the blast wave to heat and much
    higher frequency radiation is emitted from the weapon itself.

So more of the energy of the bomb remains in the x-ray or gamma portion of the spectrum---penetrating radiation, hard to shield against---in addition to the longer effective range.

Don’t overestimate education systems and peoples ability to learn from them :-)

Edit: now I'm puzzled why this is collecting downvotes. :-)

That's an odd thing to "know" considering that the amount of water vapor in the atmosphere is measured in parts per hundred, and a substantial portion of water vapor is hydrogen.

H2 is an assumption you've made. When talking about a nuclear explosion. There is hydrogen in a number of compounds (notably water and hydrogen sulfide) present in the atmosphere that could be relevant sources. The ppm being incidental is another issue. You've been unnecessarily condescending to an honest question.

That's honestly the less important part. Even if the atmosphere were pure hydrogen (whether protium or deuterium or tritium) you would not build a hydrogen bomb without its own encapsulated hydrogen fuel source.

The black magic of a hydrogen bomb is that it focuses the explosive energy of a fission bomb to ignite a fusion explosion. Doing so requires a very specific configuration; any hydrogen on the outside of the bomb, regardless of its concentration, would not reach the appropriate temperature/pressure to fuse.

Just as that person was 1 of 10,000 learning something for the first time today, I hope that today you learned that not everyone has exactly your set of knowledge. Also consider that it is quite likely that person is an expert in several things you have never even heard of.

XKCD 10,000: https://xkcd.com/1053/

Yes, inside the fusion fuel capsule there is typically a small amount of fissile material. The fusion capsule is compressed through the very strong forces from the ablation of the capsule's outer material. This compresses the fusion fuel as well as the "sparkplug" inside. The sparkplug doesn't need to contain much fissile material compared to an ordinary fission bomb core because the high degree of compression makes it easier to achieve critical conditions. The sparkplug explodes as a fission bomb, injecting heat energy into the fusion fuel capsule and driving up the conditions (temperature and pressure) which cause fusion reactions. It also injects neutrons which kickstarts the breeding of Tritium from Li-6 and Li-7.

Sometimes the "pusher" around the fusion fuel capsule is also made of fissile material which gets compressed, or imploded, just like a normal fission bomb core, but with much higher forces and so much greater efficiency and effectiveness.

Additionally, while Uranium-238 is not normally fissile it can be fissioned with high energy neutrons. The "problem" with U-238 is that the energy range of neutrons that induce fissions only partly overlaps with the natural energy range of neutrons produced by fission reactions. Meaning that on average a given neutron emitted by a U-238 fission will cause fewer than 1 additional fissions, so it can't self-sustain a neutron induced fission chain reaction (which, I guess, is a good thing, otherwise nuclear bombs would be nearly trivial to make). However, fusion reactions generate very high energy neutrons, essentially all of which can cause fission in U-238. For this reason many thermonuclear weapons have a natural or depleted Uranium casing. Fission in the casing typically doubles the yield of the weapon compared to the yield from the primary/secondary fission/fusion reactions.

All of this can be dialed to suit different desires for bomb production or yield. For example, the "Tsar Bomba" was a 100 megaton 3 stage thermonuclear warhead design, it was tested without a fissionable Uranium outer casing to avoid production of nearly 50 megatons worth of fission product fallout over the test site (which was in Russia), as a result it exploded at around 50 MT yield, almost all of which (97%) was from fusion reactions. On the other hand, you have a device like the W-88 which is an incredibly compact warhead carried on US SLBM submarines. It is a thermonuclear warhead but you could also look at it as a two stage fission-fission device with a heavily fusion boosted secondary, as most of the yield comes from fission in the secondary and the casing.