Which of the following pairs do not react with each other?

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The concept here is acid-base behavior: bases don’t neutralize each other, so they don’t typically react unless an acid or another reacting partner is present. Na2O is a basic oxide and Ca(OH)2 is a strong base. Without an acid to drive a neutralization or a redox process, there’s no driving force for a reaction between these two bases, so they remain essentially non-reactive with each other.

In the other cases, you can see clear acid-base or oxidation-reaction partners: a base reacting with an acid (silver oxide with nitric acid forms silver nitrate and water), a basic oxide reacting with an acidic oxide or gas to form a salt or carbonate (carbon dioxide with calcium hydroxide forms carbonate and water), or a base reacting with an acidic gas to form a sulfite or similar salt. Therefore, the pair that does not react is the one with two basic species.