Nasa ilalim ng silya ang pitaka ko.

Nasa is used to show location. In a sentence like this, it means something like is located in / at / on.

So instead of using a separate verb like English is, Filipino often uses nasa to express where something is. That is why you do not see a separate standalone word for is here.

Also, nasa is commonly written as one word in modern Filipino, although historically it comes from na sa.

Filipino often expresses location with a noun that names a part or area.

Here:

• ilalim = the lower part, underside, or area below
• ng silya = of the chair

So ilalim ng silya literally has the sense of the underside/below-area of the chair, which is how Filipino expresses under the chair.

Here, ng links ilalim and silya.

A helpful literal way to think about it is:

• ilalim ng silya = the underside / lower part of the chair

So in this sentence, ng works roughly like of in a literal breakdown.

This is one of several uses of ng in Filipino, so learners often see it in different roles. In this sentence, it is linking the location word ilalim to the noun silya.

Ang marks the topic of the sentence. Many beginner materials also call it the subject marker.

It is not simply the same as English the.

In this sentence, ang pitaka ko is the thing being talked about—the thing whose location is being stated.

That word order is very natural in Filipino.

The sentence is structured as:

• predicate/location first: Nasa ilalim ng silya
• topic second: ang pitaka ko

Filipino often puts the predicate before the topic. So this order is normal and common.

If you want a structure that feels more like English, you can also say:

Ang pitaka ko ay nasa ilalim ng silya.

That is also correct.

No. Ay is not required in this sentence.

You normally use ay when the topic comes first:

• Ang pitaka ko ay nasa ilalim ng silya.

But when the predicate comes first, as in your sentence, ay is not used:

• Nasa ilalim ng silya ang pitaka ko.

So nothing is missing.

Because ko is a possessive pronoun that usually comes after the noun.

So:

• pitaka ko = my wallet

You cannot normally say ko pitaka.

This noun + possessive pattern is very common in Filipino:

• bahay ko = my house
• kaibigan ko = my friend
• libro ko = my book

Yes, aking pitaka is also possible, but it is a different structure.

Both mean the same thing, but they differ in form:

• pitaka ko
• aking pitaka

For everyday speech, pitaka ko is usually the more common and neutral choice.

So in this sentence, ang pitaka ko sounds very natural.

You may hear that in casual speech or in context, but Nasa ilalim ng silya ang pitaka ko is the clearer and more standard full sentence.

Without nasa, the sentence can sound more shortened or context-dependent. For learners, it is safer to use nasa when you want to say where something is.

So if you are forming a complete sentence on your own, Nasa ilalim ng silya ang pitaka ko is the best model to follow.