18) Mg and S would be expected to react in a ratio of:
(1:1, 2:1, 1:2 or 2:3)

1:1.

Explanation:

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In this case, since magnesium, in the form that is able to react with sulfur, has an oxidation state of 2+ and sulfur 2-, because they need to be different in order to form a suitable compound; due to that equality in their oxidation states, we expect they react in a 1:1 mole ratio, according to the following example:

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