Final answer:
A) Decreases
The chemical reactivity of very active non-metals decreases as the atomic size increases due to the outer electrons being farther away from the nucleus and held less tightly, making electron gain harder.
Step-by-step explanation:
When considering the chemical reactivity of very active non-metals and its change with increasing atomic size, it generally decreases.
This is because as the atomic size increases, typically as you go down a group in the periodic table, the outer electrons are farther from the nucleus and are held less tightly. This makes it harder for these non-metals to gain electrons and hence, their reactivity decreases.
This concept mirrors the trend of the metals in groups 1 and 2, where reactivity increases down a group due to the ease of losing electrons. In contrast, for non-metals, the ease of gaining electrons diminishes with an increase in atomic size, which leads to decreased reactivity.