Niciun bec din această cutie nu este bun.

Niciun is the standard Romanian word for no / not a single / none when it goes directly before a singular noun.

• niciun bec = no bulb / not a single bulb

Romanian does not normally say nu un bec for this meaning.
Also, niciun changes for gender:

• masculine/neuter singular: niciun
• feminine singular: nicio

Since bec is masculine singular, niciun is the correct form.

This is a very common question. Romanian normally uses negative concord, which means multiple negative elements can appear together in the same sentence.

So:

• Niciun bec ... nu este bun.

is the normal Romanian structure.

In English, this might feel like a double negative, but in Romanian it is standard grammar, not a mistake.

A useful pattern is:

• Niciun/Nicio + noun + nu + verb

For example:

• Nicio carte nu este aici. = No book is here.
• Niciun student nu lipsește. = No student is absent.

Romanian often uses niciun/nicio + singular noun where English may use either singular or plural.

So Romanian prefers:

• Niciun bec ... = literally not a single bulb ...

rather than a plural structure.

This is completely normal. The focus is on each individual item, even though the overall meaning is about all of them.

Because the grammatical subject is singular:

• niciun bec = no bulb / not a single bulb

Since bec is singular, the verb is singular too:

• nu este bun

If the subject were plural, then you would use a plural verb. But with niciun + singular noun, Romanian uses singular agreement.

Din usually means from or out of, but in many contexts it also means in/from among a group or container.

Here:

• din această cutie = in this box / from this box / out of this box

So the phrase identifies which bulbs we are talking about: the bulbs from this box.

It is very natural Romanian. English may prefer in this box, but Romanian often uses din in this kind of selection meaning.

Because cutie is a feminine singular noun, and the demonstrative adjective must agree with it.

The forms are:

• masculine/neuter singular: acest
• feminine singular: această

So:

• acest bec = this bulb
• această cutie = this box

Romanian adjectives and determiners often change form to match the noun’s gender and number.

Bun means good, but in this sentence it has the practical meaning working / usable / okay.

So:

• nu este bun = is not good
• in context, especially for a light bulb, it often means doesn’t work / is defective

Its position after the verb is normal:

• nu este bun

Romanian often places predicate adjectives after forms of a fi (to be), just like English:

• is good → este bun

Yes, that is possible. Romanian word order is fairly flexible.

These are both correct:

• Niciun bec din această cutie nu este bun.
• Nu este bun niciun bec din această cutie.

The first version is usually the clearest and most neutral for learners.
The second can sound a bit more emphatic or stylistically different, but it is still natural.

Yes, bec is masculine singular here.

That matters because it affects:

• niciun (not nicio)
• bun (masculine singular form)

So the agreement is:

• niciun bec
• bec ... bun

If the noun were feminine, you would see feminine forms. For example:

• Nicio lampă nu este bună.

Here lampă is feminine, so you get nicio and bună.

Because grammatically the sentence is built around the singular expression niciun bec.

Even though the overall idea includes all the bulbs, Romanian treats it as:

• not a single bulb is good

So the adjective stays singular too:

• bun, not buni

Everything agrees with the singular noun bec.

In this sentence, the standard spelling is one word:

• niciun bec

Modern standard Romanian generally writes this determiner as one word when it means no / not any before a noun.

So here, use:

• Niciun bec din această cutie nu este bun.

not:

• Nici un bec ...

for normal standard writing.