اذا الكرسي مبلول، لا تقعد عليه هلا.

Here إذا means if.

In Levantine, it is usually pronounced iza. That is different from Standard Arabic pronunciation, where you may hear something closer to idhā.

Also, إذا can sometimes mean when depending on context, but in this sentence it is clearly conditional: if the chair is wet...

Because in Arabic, the present-tense to be is usually not said.

So:

• الكرسي مبلول literally looks like the chair wet
• but it means the chair is wet

This is completely normal in both Levantine Arabic and Standard Arabic when talking about a present state.

Because مبلول here is not directly describing the noun as part of one noun phrase. It is the predicate of the sentence.

Compare:

• الكرسي المبلول = the wet chair
• الكرسي مبلول = the chair is wet

In the first one, المبلول is an adjective attached to الكرسي, so it takes ال. In the second one, مبلول is saying something about the chair, so it does not take ال.

مبلول means wet.

It is masculine singular because it matches الكرسي, which is a masculine singular noun in Arabic.

So:

• الكرسي مبلول = the chair is wet
• الطاولة مبلولة = the table is wet

The feminine form would be مبلولة.

Because تقعد is the everyday Levantine verb you are very likely to hear in speech.

In colloquial Levantine:

• قعد / يقعد often means sit or stay

By contrast, جلس / يجلس and forms like تجلس sound more formal or closer to Standard Arabic.

So:

• لا تقعد عليه = natural spoken Levantine
• لا تجلس عليه = more formal / Standard Arabic style

This is a negative command, also called a prohibition.

In Levantine, a very common way to make this is:

• لا
  • the verb

So:

• تقعد = you sit / sit
• لا تقعد = don’t sit

Notice that this is different from an ordinary negative statement. Here لا is being used to tell someone not to do something.

عليه is made of:

• على = on
• ـه = him / it

So عليه means on him / on it.

In this sentence it means on it, referring to the chair.

Arabic uses the same attached pronoun form for him and it here. Since الكرسي is grammatically masculine, the pronoun is ـه.

If the noun were feminine, you would get عليها.

Here هلا means now, right now, or for the moment.

So it adds the idea:

• don’t sit on it now
• maybe it will be okay later, but not at this moment

If you remove هلا, the sentence becomes more general:

• إذا الكرسي مبلول، لا تقعد عليه = If the chair is wet, don’t sit on it

Also, regional variants are common. Depending on the area, you may hear words like هلّق or هسا instead.

As written, لا تقعد is addressed to one male.

Common changes are:

• to one male: لا تقعد
• to one female: لا تقعدي
• to a group: لا تقعدوا

Arabic verbs change depending on who you are speaking to, so this is something learners need to watch carefully.

Yes, this sentence is colloquial Levantine.

A more formal or Standard Arabic version would be:

إذا كان الكرسي مبلولًا، لا تجلس عليه الآن.

Main differences:

• colloquial إذا الكرسي مبلول vs formal إذا كان الكرسي مبلولًا
• colloquial تقعد vs formal تجلس
• colloquial هلا vs formal الآن

So the sentence you were given sounds like natural spoken Levantine, not textbook Standard Arabic.