"The ingredient is the jam."
Translation:L'ingrediente è la marmellata.
There is more than one masculine definite article, depending on how the next word starts. Since "ingrediente" begins with a vowel, it must be contracted.
When Duo first introduced you to the word, there should have been some kind of indication. Do you mouse over words to see what pops up?
Those times when Duo does not give the gender of a noun, I pop over to Google Translate and put in "the [plural]" and see how it comes out. That usually clears things up.
I think it should, but marmellata and confettura are not the same thing. Confettura contains more fruit. According to wordreference confettura = marmellata di frutta.
There are exceptions, but for the most part you can identify masculine and feminine nouns by how they end.
If they end in -o in the singular, they're masculine. The plural ends in -i.
If they end in -a in the singular, they're feminine. The plural ends in -e.
If they end in -e in the singular, you just need to learn it by rote.
That is a good point; I wish a reminder of this could be pinned to the top, or some basic comments room instructions, such as to first look through other answers to see if they can discover their own mistake. Also to remind people that this room isn't for reporting problems, and to use that feature instead. A little button in here to "import screenshot" from your answer would be a pretty sweet feature for certain things.