What are some chemical formulas for compounds?

Hello there!

First, we need to know what compounds are.
Compounds "are pure substances that are made up of two or more elements that are chemically combined in fixed mass ratios."

Now we need to understand what chemical formulas are.
The compounds have a chemical formula which tell us that
a) the elements that are present in the compound
b) the ratio of these elements in the compound

What are some chemical formulas for compounds?
Well, we start with water. The chemical formula for water is H2O

When we go back to the definition of compounds, it says it is when a pure substance that are made up two or more elements. So, whatever is a pure substance and it's made up of two elements. These elements are Hydrogen and Oxygen. And keep an mind that water is made up with metal plus non-metal.

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Here are one more chemical formulas for compounds
 Sodium Chloride = NaCI

I included a picture that might help you too. (Credit to google image)
 

The answer options is d