Consider the following elements in their stable forms:

Nitrogen

lodine

Fluorine

Bromine

Then for each of the following questions, enter the number listed $(1-4)$ before the element, for elements that satisfy the criterion. Enter the number$($s$)$ in order with no

separators. If none, type "none" or leave blank.

$($a$)$ Which of these elements have allotropes?

$($b$)$ Which of these elements exist as diatomic molecules?

$($c$)$ Which of these elements exist as a metallic lattice?