1. What kind of favorite movies do you like?

2. What kind of favorite movie do you like?

- I like horror movies.

(Are the questions and answer correct? Do we have to use the plural form, 'kinds'?)

3. What is your favorite kind of movies/movie?

- 4. It is horror movies.
- 5. It is horror movie.
- 6. It is a horror movie.
(Which answer is right?)

Yes, kinds of movies

Preferable would be, I like horror movies.

I like a horror movie

Of those, 6 would be the best.

1 and 2 are awkward. Either remove the word "favorite" or write the sentence like this:

What kinds of movies are your favorites?

The questions and answers you provided are correct. However, let me explain the usage of plurals and singulars in these sentences.

1. "What kind of favorite movies do you like?" is grammatically correct. In this sentence, we are asking about the various types or categories of movies that are favorites for you. Since there can be more than one favorite movie, we use the plural form "movies."

2. "What kind of favorite movie do you like?" is also grammatically correct, but it implies that there is only one favorite movie. In this case, we use the singular form "movie."

Now let's move on to your subsequent questions:

3. "What is your favorite kind of movies/movie?" is grammatically correct. Here you are asking about the favorite genre or category of movies that you like. Again, we can use either the plural form "movies" or the singular form "movie" depending on whether you have multiple favorite genres or just one.

Out of the options you provided:

4. "It is horror movies" is incorrect because here we are talking about a single favorite genre, so we should use the singular form "movie."

5. "It is horror movie" is also incorrect because it lacks an article. We need to use "a" before "horror movie."

6. "It is a horror movie" is the correct answer. By using the article "a," we are specifying that the favorite genre is a single horror movie.

Therefore, the correct answer is: "It is a horror movie."