I have found this where it explains the usage of het and de: https://forum.duolingo.com/comment/3732938/Grammar-De-Het-Een but in this case I don't understand why it's de since peper is a neuter noun if I'm not wrong.
Why not "het peper"? I thought it was a neuter noun, as it says here: https://forum.duolingo.com/comment/3732938/Grammar-De-Het-Een
It's not a neuter noun.
Note that most "rules" for whether something is a de-noun (originally a masculine or a feminine noun) or a het-noun (originally a neuter noun) aren't hard rules. They are more like guidelines or rules of thumb. It's better to just try to remember which nouns go with "het".
If you're unsure of the gender of the noun, you can check vandale.nl.
Dont try to explain the articles. Have you ever learned French ?(no idea if atleast some French is mandatory in other countries. In the netherlands you get atleast 1 year. Or atleast that was always the case I think quite a bit changed right after I left)
Did you ask (yourself or others) then why it was le and not la?
The articles are what they are. Why is english plant not plond...