Njihov plan je dobar.

Njihov means their. It is a possessive word, like English my, your, his, her, our, their.

So:

• njihov plan = their plan

In Serbian, this kind of word behaves like an adjective, so it changes form to match the noun it describes.

Because njihov has to agree with plan.

Plan is:

• masculine
• singular
• nominative

So the possessive adjective also appears in the masculine singular nominative form:

• njihov plan = their plan

If the noun were different, the form would change:

• njihova ideja = their idea (ideja is feminine)
• njihovo dete = their child (dete is neuter)
• njihovi planovi = their plans (plural)

For the same reason: dobar agrees with plan.

Since plan is masculine singular, the adjective is also masculine singular:

• dobar plan = a good plan
• plan je dobar = the plan is good

Compare:

• ideja je dobra = the idea is good
• rešenje je dobro = the solution is good
• planovi su dobri = the plans are good

Je means is. It is the 3rd person singular present form of biti = to be.

So the sentence breaks down as:

• Njihov = their
• plan = plan
• je = is
• dobar = good

So literally: Their plan is good.

Normally, no. In a standard full sentence like this, je is needed.

• Njihov plan je dobar. = correct

Without je, it would sound incomplete in ordinary standard Serbian.

You may sometimes see the verb omitted in headlines, notes, or very informal styles, but learners should use je here.

Plan is in the nominative singular.

That is because it is the subject of the sentence:

• Njihov plan = the thing being talked about

In a simple X is Y sentence, the subject is in the nominative. Here, dobar is a predicate adjective describing that subject, so it matches the nominative masculine singular noun plan.

No. Serbian does not use articles like English a/an and the.

So plan can mean:

• a plan
• the plan

The exact meaning depends on context.

That is why Njihov plan je dobar can naturally mean Their plan is good without any separate word for the.

Yes. Serbian word order is more flexible than English word order.

The neutral, most straightforward version is:

• Njihov plan je dobar.

But other orders are possible for emphasis, for example:

• Dobar je njihov plan. = Their plan is good / It is their plan that is good.
• Plan im je dobar. = Their plan is good.

Even though the order can change, the basic meaning stays similar because the grammar endings help show the relationships.

For a learner, Njihov plan je dobar is the safest and most neutral order.

Because possessive words like njihov usually come before the noun they describe, just like in English:

• their plan
• njihov plan

This is the normal order in Serbian:

• possessive + noun

So njihov plan is the expected and natural phrasing.

No.

• njihov = their
• njegov = his

This is a very common confusion for learners because the words look similar.

Compare:

• Njihov plan je dobar. = Their plan is good.
• Njegov plan je dobar. = His plan is good.

For her, Serbian usually uses:

• njen
• sometimes also njezin depending on region/style

A rough pronunciation is NYEE-hov.

A few key points:

• nj is a single sound, like Spanish ñ in señor, or roughly ny in canyon
• j in Serbian is pronounced like English y
• h is pronounced, unlike in many English words

So:

• njihov ≈ NYEE-hov

The whole sentence can be approximated as:

• NYEE-hov plahn yeh DOH-bar

This is only an approximation for English speakers, but it helps as a starting point.

The possessive and the adjective would both change to match the new noun.

Examples:

• Njihova ideja je dobra. = Their idea is good.
• Njihovo rešenje je dobro. = Their solution is good.
• Njihovi planovi su dobri. = Their plans are good.

Notice the pattern:

• masculine singular: njihov ... dobar
• feminine singular: njihova ... dobra
• neuter singular: njihovo ... dobro
• plural masculine: njihovi ... dobri

This agreement is one of the most important features of Serbian grammar.

Sometimes Serbian can omit a noun if the meaning is clear from context, but in a basic sentence like this, keeping plan is the most natural and easiest choice.

So:

• Njihov plan je dobar. = clear and natural

You can build shorter sentences in context, but for learning purposes it is best to use the full sentence first.