O i get it it does not stik on metal eater way
Answer:

Explanation:
We are given the formula:

This is a molecular formula, because it contains nonmetals.
1. Name the first element
The first element is phosphorous (P). Since this is the first element and there is only one, we don't need a prefix.
2. Second element
The second element is chlorine (Cl). It has a subscript of 5, so we must add the prefix of <u>hepta</u>-.
- Phosphorous heptachlorine
Add the ending of -ide.
- Phosphorous heptachloride
The prefix used for the second element is hepta. The compound name is phosphorous heptachloride.
The relative mass of each element can be found from the periodic table (the larger number). For instance, P2O5, P = 31.0 O = 16.0, thus the formula mass (Mr) is 2(31) + 5(16) = 142 amu (atomic mass unit). I used a not really specific periodic table. Maybe your teacher is referring to open Schoology (a website where teacher can post files or announcements to students in his or her class). Sorry if i got something mistaken.
I believe it's answer #3. Logically, at least.
You can test #1 through trial and error.
You can experiment #2 also through trial and error.
You cannot test #3 through trial and error, because that would be catastrophic.
You can test #4 through a survey and individual study and data collection.
Sorry, the correct answer is A. 3.4 x 10 - 24
Hope I helped ; )