There is no law against writing about how to make explosives. I just searched Amazon under "chemical engineering" for "explosives" and got 190 hits. I suppose not all these books are how-to recipes, but many of them are.
Mystery writers routinely talk about how to commit a murder and get away with it.
In any case, there's a big difference between saying "napalm makes an effective weapon" and actually telling someone where to obtain it and how to make a working bomb from it. If your story actually goes into all the details about how to make a usable bomb -- where to obtain the necessary chemicals and mechanical parts, how to prepare the chemicals, how to assemble all the parts, etc -- I'd say don't do that because it would be incredibly boring to any reader who is NOT planning an actual terrorist attack. Which I'd hope would be the vast majority of your readers. If your idea of a gripping dramatic novel is, "Bob bought a 50 foot spool of 14 gauge solid copper wire. He cut three lengths of wire from this spool, one three feet long, one four feet, and one six feet. He stripped a half inch of the insulation off of each end of all three pieces. He then took the shortest piece of wire and bent the end into a loop by wrapping it around a screwdriver. To his dismay, this made a loop that was too big for the screw head on the connector and it slipped off. He cried out in frustration ..." -- well, I think you need to rethink what will appeal to your readers.