Karatasi zilitawanyika sakafuni nilipofungua dirisha.

In Swahili, some nouns have the same form in both singular and plural. Karatasi is one of them. The verb agreement shows the number:

• karatasi ilitawanyika = the paper scattered
• karatasi zilitawanyika = the papers scattered

So here, zi- on the verb tells you that karatasi is plural.

Because karatasi belongs to noun class 9/10. In the plural, class 10 nouns take the subject marker zi-. Swahili verbs must agree with the noun class of the subject, so the verb begins with zi-.

That is why you get:

• zi-li-tawanyika = they scattered

and not a subject prefix like wa- or i-.

It can be broken down like this:

• zi- = subject marker for class 10 plural
• -li- = past tense
• -tawanyika = scatter, become scattered

So zilitawanyika means they scattered or they became scattered.

It can feel like either in English, depending on context. The key point is that -tawanyika is intransitive: it describes what happened to the papers, not who did it.

Compare:

• Mtu alitawanya karatasi. = Someone scattered the papers.
• Karatasi zilitawanyika. = The papers scattered / became scattered.

So in your sentence, the focus is on the papers and what happened to them, not on an agent.

It breaks down like this:

• ni- = I
• -li- = past tense
• -po- = when / at the time when
• -fungua = open

So literally it is something like I-past-when-open, which Swahili uses to mean when I opened.

Here, -po- creates a time clause. It gives the meaning when or at the time when.

Compare:

• nilifungua = I opened
• nilipofungua = when I opened

This is a very common Swahili way to express when without adding a separate word.

The ending -ni makes a locative form.

• sakafu = floor
• sakafuni = on the floor / at the floor

Swahili locatives are broader than English prepositions, so -ni can cover meanings that English separates into in, on, or at. In this sentence, the natural English choice is on the floor.

Swahili normally does not use articles like English a, an, or the. Whether something is definite or indefinite is understood from context.

So:

• dirisha can mean a window or the window
• karatasi can mean paper, papers, the paper, or the papers

The surrounding context tells you which meaning is intended.

Because the object noun is stated directly after the verb, an object marker is not required.

So nilipofungua dirisha is a normal and straightforward structure.

If you used an object marker, it would agree with dirisha as a class 5 noun, giving a form like nilipolifungua = when I opened it / the window. But for learners, the version without the object marker is the basic pattern to expect when the object noun is present.

Yes. Swahili allows that very naturally. You can also say:

• Nilipofungua dirisha, karatasi zilitawanyika sakafuni.

That works just like English:

• The papers scattered on the floor when I opened the window
• When I opened the window, the papers scattered on the floor

Both orders are normal; the difference is mostly one of focus and style.

Yes, but it is less compact. Swahili often prefers to put the idea of when directly into the verb, as in nilipofungua.

A longer version would be:

• Wakati nilipofungua dirisha, karatasi zilitawanyika sakafuni.

That is possible, but the original sentence is shorter and very natural.