אם הכוס לא נקייה, אפשר להחליף אותה.

In Hebrew, the verb to be is usually not stated in the present tense.

So:

• הכוס נקייה = the cup is clean
• literally: the cup clean

That is completely normal Hebrew.
If you want past or future, Hebrew does use forms of to be:

• הכוס הייתה נקייה = the cup was clean
• הכוס תהיה נקייה = the cup will be clean

So in your sentence, לא נקייה simply means is not clean, even though is is not written.

The ה־ at the beginning is the Hebrew definite article, meaning the.

• כוס = a cup / cup
• הכוס = the cup

Since the sentence is talking about a specific cup, Hebrew uses הכוס.

Because כוס is a feminine noun, and adjectives in Hebrew must agree with the noun in gender and number.

So:

• masculine singular: נקי = clean
• feminine singular: נקייה = clean

Examples:

• שולחן נקי = a clean table
  (שולחן is masculine)
• כוס נקייה = a clean cup
  (כוס is feminine)

That is why נקייה is the correct form here.

You usually have to learn the gender of each noun, but many common nouns are familiar through repeated exposure. כוס is one of those nouns that is simply feminine.

You can tell in this sentence because the adjective and pronoun both agree with it:

• כוס ... נקייה
• אותה = it/her in the feminine singular form

So the sentence itself gives you clues that כוס is feminine.

אם means if.

So:

• אם הכוס לא נקייה... = If the cup is not clean...

It introduces a condition, just like if in English.

אפשר is an impersonal word meaning something like:

• it is possible
• one can
• you can
• it’s possible to

So:

• אפשר להחליף אותה literally = it is possible to replace it
• more natural English = you can replace it or it can be replaced

It does not refer to a specific person doing the action. It is a general, impersonal statement.

Because אפשר is often followed by an infinitive to say that an action is possible.

Pattern:

• אפשר + infinitive

Examples:

• אפשר ללכת = it’s possible to go / you can go
• אפשר לשבת = you may sit / you can sit
• אפשר להחליף אותה = it’s possible to replace it

So this is a very common Hebrew structure.

להחליף is the infinitive form of the verb החליף = to replace / exchange.

In Hebrew, infinitives usually begin with ל־, often equivalent to English to:

• לכתוב = to write
• לאכול = to eat
• להחליף = to replace

So the ל־ here is just part of the infinitive form.

אותה is the direct object pronoun meaning her / it for a feminine singular noun.

Since כוס is feminine singular, Hebrew uses אותה to mean it.

So:

• להחליף אותה = to replace it

Compare:

• masculine singular: אותו = him / it
• feminine singular: אותה = her / it

Even though English says it, Hebrew still chooses masculine or feminine based on the noun’s grammatical gender.

Because replace takes a direct object, not an indirect one.

• אותה = direct object pronoun: it / her
• לה = indirect object pronoun: to her

In Hebrew:

• להחליף אותה = replace it
• לתת לה = give to her

So אותה is correct because the cup is the thing being replaced directly.

Yes, it is very normal.

The sentence has two parts:

1. אם הכוס לא נקייה = if the cup is not clean
2. אפשר להחליף אותה = it’s possible to replace it / you can replace it

This is a common pattern:

• אם... , ...
• If..., ...

So the overall structure is very natural Hebrew.

Yes. Both are grammatical, but they differ in style.

• לא נקייה is more common in everyday spoken Hebrew
• אינה נקייה is more formal or written

So:

• אם הכוס לא נקייה... = everyday, natural speech
• אם הכוס אינה נקייה... = more formal

For most learners, לא is the form you will hear much more often in regular conversation.

It is usually pronounced roughly as ne-kee-YA.

A simple breakdown:

• נְ = ne
• קִי = ki
• יָה = ya

So: ne-ki-ya

The stress is usually on the last syllable: ne-ki-YA.

Yes, depending on context, English may translate it in different ways.

Literally, Hebrew says something like:

• it is possible to replace it

In natural English, that might become:

• you can replace it
• it can be replaced

The Hebrew wording is impersonal, so it does not specifically say who replaces it. That flexibility is normal with אפשר.

It can mean both, depending on context.

להחליף can be used for:

• replace
• exchange
• swap

In a sentence about a cup in a restaurant or café, it often suggests something like:

• replace it with another one
• exchange it

So the exact English wording depends on the situation, but the Hebrew verb is the normal choice here.