There's nothing wrong with the question... it's a matter of physics. Now if he said "I want to drop a gigaton bomb on country "B" and kill 'em all" then yeah, there are issues.
The answer is yes, it is theoretically possible. But it'd never get airborne, being too massive. Big hydrogen bombs are staged devices. Add more stages, get more yield. The power comes from tritium, lithium deuteride, and other fusable isotopes, not plutonium or unranium. The latter two form just the fission trigger, the fuse to get the fusion going.
Little known fact - the temperatures created by a primitive fission bomb are the same or even hotter than the core of the sun. Fusion is very natural, it's all over the universe, but fission as a BOMB is an entirely man-made thing.
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It's worthwhile to add that a falling comet or big asteroid would probably crack a gigaton, and we've likely had several of these in Earth's history. It would suck, but there'd be survivors.