La palabra “libros” está en plural y es masculina.

Because the sentence is talking about one word: the word libros.

So la palabra means the word, and palabra is a feminine singular noun in Spanish. That is why you get:

• la palabra = feminine singular
• libros = the specific word being discussed

In other words, the structure is:

• La palabra libros... = The word libros...

You are not saying that libros itself is feminine. You are saying that the noun palabra is feminine.

Because masculina agrees with palabra, not directly with libros.

In Spanish, adjectives usually agree with the noun they describe. Here, the grammatical subject is la palabra, which is feminine singular, so the adjective is also feminine singular:

• la palabra ... es masculina

This means the word is masculine.

A very useful comparison:

• La palabra libros es masculina.
• El sustantivo libros es masculino.

Both mean basically the same thing, but:

• palabra is feminine → masculina
• sustantivo is masculine → masculino

Spanish often uses different verbs for these ideas:

• estar en plural / estar en singular for the form a word appears in
• ser masculino / ser femenino for grammatical gender

So:

• está en plural = it is in the plural form
• es masculina = it is a masculine word

A simple way to think about it:

• plural is treated as the form the word currently has
• masculine/feminine is treated as a grammatical category the word belongs to

That is why the sentence naturally uses both estar and ser.

Because libros is the plural form of libro.

In Spanish, many nouns form the plural by adding -s:

• libro = book
• libros = books

So the ending -s tells you that the word is plural.

The singular form is libro.

So:

• libro = singular
• libros = plural

This is one of the most regular noun patterns in Spanish.

The base noun is libro, and libro is masculine.

You can see that from the article it normally takes:

• el libro = the book
• los libros = the books

Masculine singular nouns usually go with el, and masculine plural nouns usually go with los.

Also, nouns ending in -o are often masculine, although that is a tendency, not an absolute rule.

No. It means grammatically masculine, not biologically male.

Spanish nouns have grammatical gender:

• masculine
• feminine

This is a grammar category. It does not mean that a book is male.

For example:

• libro is masculine
• mesa is feminine

That is just how the language classifies the nouns.

Because it is being mentioned, not used in its normal meaning.

The sentence is talking about the word libros itself, not about actual books. This is why Spanish often writes the word in quotation marks, italics, or another marked style.

Compare:

• Los libros están en la mesa.
  Here libros is being used normally and means actual books.

• La palabra libros está en plural.
  Here libros is being talked about as a word.

Because the sentence is naming the word libros, not using it as a normal noun inside the sentence.

If you said:

• la palabra libros

you mean the word libros

But if you said:

• la palabra los libros

you would be talking about the whole expression los libros, not just the single word libros.

So the article is left out because only the noun form itself is being discussed.

Because there is only one word being discussed.

The word itself happens to be in a plural form, but it is still just one word. So:

• la palabra = singular
• libros = a plural form

This is similar to English:

• The word books is plural.

books is plural, but word is singular.

Because está is the verb form of estar and it is written with an accent on the final a.

This helps show the correct stress and also distinguishes it from esta, which can be:

• a demonstrative word such as this
• part of other structures depending on context

So:

• está = is from estar
• esta = this / related demonstrative use

The accent is important and should be written.

Yes, absolutely.

That version is also correct and may even feel clearer in a grammar explanation.

Notice the agreement change:

• La palabra libros ... es masculina
• El sustantivo libros ... es masculino

Why the change?

• palabra is feminine → masculina
• sustantivo is masculine → masculino

So both are correct; the adjective changes to match the noun you use to introduce libros.