In the presence of a base, blue litmus paper will .
O turn purple
stay blue
to turn red

In the presence of a base the blue litmus paper would remain blue.

Explanation:

This is because the litmus paper will react depending on the pH of the solution added. If the solution is acidic pH < 7, the litmus paper will turn red. If the solution is basic, pH > 7  the litmus paper will turn blue. If the litmus paper is blue when a base is added it will remain blue.

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