Birika na kadi ya ufunguo ziko chumbani.

Because the subject is two things together: birika + kadi ya ufunguo.

Even though each noun is singular by itself, they are joined by na (and), so the whole subject is plural: the kettle and the key card. That is why Swahili uses a plural agreement form.

With mixed non-human nouns like these, Swahili commonly uses zi- as the agreement, so ziko means they are / they are located.

Ziko is a location form of to be.

In this sentence, it means something like:

• are
• are there
• are located

So Birika na kadi ya ufunguo ziko chumbani is literally structured like:

• Birika na kadi ya ufunguo = the kettle and the key card
• ziko = are located / are
• chumbani = in the room

So ziko is not just a general are; it is especially natural when talking about where things are.

Here, na means and.

It links the two nouns:

• birika = kettle
• kadi ya ufunguo = key card

So:

• Birika na kadi ya ufunguo = the kettle and the key card

Swahili na can also mean with in other contexts, but in this sentence it is simply joining two items.

This is an associative / of-construction.

• kadi = card
• ya = of
• ufunguo = key

So literally it is card of key, but in natural English that becomes key card.

The important point is that ya agrees with kadi, not with ufunguo. Since kadi belongs to the noun class that uses ya in this pattern, you get:

• kadi ya ufunguo

This structure is very common in Swahili.

Because the connector has to match the noun being described, which is kadi.

In Swahili, of-type connectors change form depending on noun class. For kadi, the matching form is ya.

So:

• kadi ya ufunguo = key card

If the head noun were in a different noun class, the connector might be different.

In Swahili, location is often built into the noun itself by adding -ni.

• chumba = room
• chumbani = in the room / at the room / inside the room

So the -ni ending is doing the work that English often does with prepositions like in, at, or to.

That is why Swahili does not need a separate word for in here.

The main ones are:

• birika — usually treated as a class 5 singular noun
• kadi — a class 9/10 noun
• ufunguo — a different noun class again

This matters because Swahili grammar uses noun classes for agreement. That affects forms like:

• liko for a singular birika
• iko for a singular kadi
• ziko for a plural or mixed non-human subject like the one in this sentence

So noun class is one big reason the sentence looks the way it does.

The verb would change to match that one noun.

For example:

• Birika liko chumbani. = The kettle is in the room.
• Kadi ya ufunguo iko chumbani. = The key card is in the room.

Notice:

• birika takes liko
• kadi takes iko

But when you put them together with na, the sentence uses ziko.

Here, kadi is singular: it means one card.

A tricky point is that many class 9/10 nouns look the same in singular and plural. So kadi can mean card or cards, depending on context and agreement.

Compare:

• Kadi iko mezani. = The card is on the table.
• Kadi ziko mezani. = The cards are on the table.

In your sentence, kadi ya ufunguo is singular by itself, but the whole subject is plural because it is joined with birika.

Because ufunguo is the singular form meaning key, while funguo is plural, keys.

So:

• ufunguo = key
• funguo = keys

In kadi ya ufunguo, the idea is key card, referring to the type or function of the card, so the singular ufunguo is natural.

Because Swahili does not normally use articles the way English does.

English distinguishes:

• a kettle
• the kettle

Swahili usually just says:

• birika

The exact meaning depends on context. So Birika na kadi ya ufunguo ziko chumbani could be understood as:

• The kettle and the key card are in the room
• or, depending on context, A kettle and a key card are in the room

Usually the situation makes it clear.

The neutral, straightforward order here is:

• subject + verb + location

So:

• Birika na kadi ya ufunguo ziko chumbani.

That is the most natural basic order for a learner to use.

Swahili does allow some flexibility, especially with location words, but changing the order usually changes the emphasis, not the core meaning. So for now, it is best to learn this sentence as a standard pattern:

• [things] + ziko + [place]