What events separate geologic time into eras and periods

A formula unit represents the simplest ratio of elements in a  

✔ crystal

of an ionic compound.

A crystal is made up of  

✔ many atoms that are arranged in a regular pattern.

There are two magnesium ions for every two sulfide ions in magnesium sulfide. The ratio of Mg to S in the formula unit is  

✔ 1:1

.

Explanation:

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