Learn Hardcore Italian: Questo esercizio è importantissimo.

Because it’s the third-person singular present form of the verb essere (to be), and the grave accent distinguishes it from the conjunction e (and).

What part of speech is questo in this sentence?

Questo is a demonstrative adjective (determiner) meaning this. It directly modifies the masculine singular noun esercizio.

Why don’t we use the definite article il before esercizio?

Because questo already functions as the determiner for esercizio; in Italian you can’t have both a demonstrative and a definite article together—questo on its own conveys both this and the.

Why is it questo and not quest’ (with an apostrophe) before esercizio?

In standard Italian, the full form questo is used as an adjective before a noun. The contracted form quest’ appears only in very colloquial speech or when questo replaces the noun entirely (as a pronoun).

How is importantissimo formed from importante?

You take the adjective importante, drop its final -e, and add the suffix -issimo. This operation creates the absolute superlative, giving the sense of extreme intensity.

What does the suffix -issimo add to the meaning?

The suffix -issimo forms the absolute superlative, intensifying the adjective to mean extremely or very, very.

Why is there a double s in importantissimo?

The suffix -issimo itself contains two s letters. When attached to the stem important-, they remain doubled, resulting in importantissimo.

Could we also say questo esercizio è molto importante instead of importantissimo?

Yes. Molto importante is a perfectly normal way to say very important. Importantissimo is simply a stronger, single-word way to express a higher degree of importance.

Why is importantissimo placed after è and not directly before esercizio?

Here importantissimo functions as a predicative adjective (a complement to the verb essere), so it follows è. If you want it attributively, you can say questo importantissimo esercizio, placing it before the noun.