Learn Farsi: آیا این محرک قوی است؟ نه، هیچ قوی نیست. - Is this stimulus strong? No, it is not strong at all.

Here, hich is used as an adverb directly modifying the adjective qavi (strong). When placed independently before an adjective or adverb and paired with a negative verb like nist (is not), it acts as an absolute negation. So hich qavi nist translates to it is not strong at all.

Could I use aslan instead of hich to mean not at all in this context?

Yes, saying aslan qavi nist is perfectly correct and very common. Using hich in this specific adverbial way serves the exact same purpose as aslan, giving a natural, absolute, and emphatic tone to your negative statements.

The subject in moharrek is missing in the second half. Is it normal to just say hich qavi nist?

Yes, Farsi frequently drops pronouns and subjects once they are established in context. Since the first sentence explicitly asks about this stimulus, repeating it in the answer would sound clunky and unnaturally repetitive.

Does the word moharrek only mean stimulus in a scientific sense?

Not necessarily. While it works perfectly as stimulus in medical or psychological contexts, moharrek comes from an Arabic root relating to movement. In everyday Farsi, you will often see it used to mean a motive, an incentive, or the driving force behind someone's actions.