8. Which of the following is an example of a molecule of element?

To determine which of the following is an example of a molecule of an element, we need to understand what a molecule is and what an element is.

A molecule is a group of two or more atoms that are chemically bonded together. An element, on the other hand, is a pure substance that consists of only one type of atom.

Now, let's examine the options provided and determine if they meet the criteria of being a molecule of an element:

1. H2O (water) - This is not an example of a molecule of an element because it consists of two different types of atoms: two hydrogen atoms and one oxygen atom.

2. O2 (oxygen gas) - This is also not an example of a molecule of an element because it consists of two oxygen atoms bonded together. While oxygen is an element, O2 is a molecule of oxygen, not a molecule of an element.

3. NaCl (sodium chloride) - This is not an example of a molecule of an element because it consists of two different types of atoms: one sodium atom and one chlorine atom.

4. N2 (nitrogen gas) - This is an example of a molecule of an element. It consists of two nitrogen atoms bonded together, and nitrogen is an element.

Therefore, the correct answer is option 4, N2 (nitrogen gas), as it is an example of a molecule of an element.