Yes it's the present tense.
The present tenses of "clean" are: I clean You clean He/she/it cleans We clean They clean
No, will clean is future tense. Clean is present tense.
The present participle is cleaning.
The present simple tense of the verb "clean" is "clean" for the pronouns I, you, we, and they (e.g., I clean the house every day). For the pronouns he, she, and it, it is "cleans" (e.g., She cleans the dishes after dinner).
The present perfect tense of clean is:I/You/We/They have cleaned.He/She/It has cleaned.
It is "clean/cleans".
I/We/You/They have been cleaningHe/She/It has been cleaning
cleaning
Clean is not past perfect. It's present simple. The past perfect tense of clean is had cleaned.
smart and clean
Clean is not past tense, it's present tense. The past tense is cleaned.
Yes. The air is never clean.