गुब्बारों की सजावट से कमरा सजाओ।

Because गुब्बारा is being used in the plural oblique form.

Hindi nouns often change form before a postposition or in a possessive phrase. Here, गुब्बारों appears before की, so it becomes oblique:

• singular direct: गुब्बारा
• plural direct: गुब्बारे
• plural oblique: गुब्बारों

So गुब्बारों की सजावट means something like the decoration of balloons or balloon decoration.

Because का / की / के agrees with the thing being possessed, not with the possessor.

In गुब्बारों की सजावट:

• गुब्बारों = of balloons
• सजावट = decoration

Since सजावट is a feminine singular noun, the possessive marker must be की.

Compare:

• लड़के का कमरा = the boy’s room
• लड़के की किताब = the boy’s book
• लड़के के दोस्त = the boy’s friends

So here: गुब्बारों की सजावट because सजावट is feminine.

सजावट is a noun meaning decoration, decor, or the act/result of decorating.

It comes from the same root as सजाना, which means to decorate.

So in this sentence you have both:

• सजावट = decoration (noun)
• सजाओ = decorate! (verb, command)

That is why the sentence can feel repetitive to learners, but it is normal:

• गुब्बारों की सजावट = balloon decoration
• कमरा सजाओ = decorate the room

Here से means with, by means of, or using.

It marks the means or material used to do the action.

So:

• गुब्बारों की सजावट से = with balloon decoration / using balloon decorations

This is a very common use of से in Hindi:

• चाकू से काटो = cut with a knife
• कलम से लिखो = write with a pen
• फूलों से सजाओ = decorate with flowers

Because Hindi often leaves out को with a direct object, especially when the object is inanimate and general.

So कमरा सजाओ is perfectly natural and means decorate the room.

You could also say कमरे को सजाओ, but that sounds a bit more marked or emphatic in many contexts.

Compare:

• कमरा सजाओ = decorate the room
• कमरे को सजाओ = decorate the room (with a little more focus on the room)

Both are grammatical.

सजाओ is the imperative form of सजाना used with tum.

So it is a command or instruction directed to someone addressed as tum.

Related forms:

• सजा = decorate! (to tu, very informal)
• सजाओ = decorate! (to tum)
• सजाइए / सजाइये = please decorate (to aap, polite/formal)

So this sentence sounds like an instruction such as one teacher, friend, parent, or organizer might give:

• गुब्बारों की सजावट से कमरा सजाओ।

No. It means decoration involving balloons or balloon decoration, not decorate the balloons.

If you wanted to say decorate the balloons, you would say:

• गुब्बारों को सजाओ।

In your sentence, गुब्बारों की सजावट is a noun phrase referring to the decoration itself, and then से shows that this decoration is the means used to decorate the room.

Yes, absolutely. In fact, गुब्बारों से कमरा सजाओ is simpler and often more natural in everyday speech if you mean decorate the room with balloons.

The difference is roughly:

• गुब्बारों से कमरा सजाओ = decorate the room with balloons
• गुब्बारों की सजावट से कमरा सजाओ = decorate the room with balloon decorations / using balloon decor

So the original sentence sounds a bit more descriptive or formal, while the shorter version is more direct.

Not completely, but the verb usually stays near the end.

The given order is:

• गुब्बारों की सजावट से = with balloon decoration
• कमरा = room
• सजाओ = decorate

This is a normal Hindi structure: means/instrument + object + verb.

You could also hear:

• कमरा गुब्बारों की सजावट से सजाओ।

That still works, because Hindi allows some flexibility in word order. But सजाओ usually remains at the end.

It is understandable and grammatically fine. It sounds like an instruction, maybe in a school activity, party plan, or decorating guide.

But in everyday conversation, many speakers would probably use a simpler version such as:

• गुब्बारों से कमरा सजाओ।
• कमरे को गुब्बारों से सजाओ।

If you want a polite version, you could say:

• गुब्बारों से कमरा सजाइए।

So the original sentence is natural enough, but slightly more formal or elaborate than the most common conversational wording.