"Yang mana tomat yang termerah itu?"

Translation: Which one is the reddest tomato?

[kuyaC]

Why is there "itu" in the Indonesian sentence? Isn't it useless?

[Ms.Fixer]

One of the functions of "itu" or "ini" is "is/are/am". "Itu" in this particular sentence is a casual version of "adalah". "Itu/ini" makes the tone of the whole sentence stronger or softer -- It totally depends. So, "itu" is not useless here :) But you can omit "itu/ini" without significantly change the meaning.

You'll find the same structure in other Duolingo lessons (you'll probably find them in the later stage):

"Kamu INI sangat memalukan." = "You are very embarrassing." (itu = are, and the speaker is strongly condemning. The speaker and "kamu" are likely to be in a close distance. So, "ini" instead of "itu" is chosen.)

"Apakah energi ITU?" = "What is energy?" (itu = is; the speaker is asking the "general" concept of energy. It doesn't mean "that" energy.)

Re: these two sentences, I got answers from Indonesian native speakers. So, I'm almost sure that this tomato sentence has the same structure.

[yipivan]

I think the sentence is parsed in this way:

• Yang mana [tomat [yang termerah] itu]?

Hence a clumsy literal translation is

• Which is the tomato that is the reddest?

[laviedulinguiste]

This answer is not very colloquial. Another possible solution should be "Which tomato is the reddest?"

[noey536981]

Two yang's and a random itu??? Now we're getting into professional bahasa indonesia

[Sam67858]

Or “Which tomato is the reddest one?”

[tuanle163158]

what's "itu" doing?

[volumniax]

"One" is acceptable... but kind of redundant. I would be more likely to say either "Which one is the reddest" or "Which is the reddest tomato."

[navysa]

Frankly, we don't speak like this in daily conversation. Instead, we will say 'Tomat mana yang paling merah?'