Prefix -un and suffix -ness

I like quite rooms. So ... is very important to me.

This condition is good because you can see your things tidy.

This state makes you feel happy.

She listens to everyone's problems. She expresses her k...

When we use the prefix -un in a word like "happy", are we changing the word category or does it continue being an adjective?

I am very bad at playing sports. I am weak. That's my ...

My room is a mess, it isn't tidy. It's ...

When someone is ill, that person has an ...

They never smile or say hello. They're very ...(not friendly).

The game hasn't got fair rules. It is ...

The opposite of helpful is...

The word "unfriendly" means not ...?

I am writing a sad story. It's main topic is ...

When we add the suffix -ness to a word like happy, we have a new word category. Is it an adjective, a noun or a verb?