You have a passing familiarity with chemical reactions and compounds from your upbringing or exposure to someone who worked with chemicals. Maybe you grew up around a family member who was a chemist, or you spent time in an environment where basic chemical knowledge was necessary.
You're not a professional chemist by any means, but you've picked up some basic understanding of how chemicals work and their general properties. Perhaps your parents owned a small lab and you helped out occasionally, or you had enough curiosity to tinker with simple chemical reactions on your own.
As a result of your passing familiarity with chemistry, you have a few Knacks up your sleeve that can come in handy in a variety of situations. You know how to identify different chemicals, for example, or how to create basic chemical reactions.
You still have a ways to go before you are as experienced or knowledgeable as a true professional, but you have started your journey.
Choose one of the following skill boons.
Lab accident on Kovac Station: the thermal cycler destabilised, the catalyst started chain-reacting, and everyone else in the room froze. You grabbed the quench agent, neutralised the runaway exotherm, and vented the fumes before the fire suppression even triggered. Chemistry teaches you that every second of hesitation is a second closer to an uncontrollable outcome.
Your uncle ran a pest control outfit on a station where the pests had evolved resistance to everything legal and most things that weren't. By fourteen you could identify organophosphate families by smell, calculate lethal dosages per kilogram of body mass, and explain exactly how curare analogues interrupt neuromuscular signalling. You know what kills things, what almost kills things, and the razor-thin margin where medicine lives.
The pharmacy on Relay Station Nine ran out of standard analgesics during a transit strike, and somebody had to synthesise replacements from raw compounds in storage. That somebody was you, working off a pharmacopoeia you'd memorised out of boredom. Every dosage was calculated twice, measured three times, and tested on yourself first. The strike lasted nine days. Nobody died on your watch.