Identify the structure of elements.
Consider the following elements in their stable forms:
1. Potassium
2. Krypton
3. Oxygen
4. Neon
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?
