Answer :
There are 0.00045 moles of sodium hydroxide that were added in the solution.
From the question, we have the following information;
Volume of sodium hydroxide = 0.90 mL or 0.00009 L
Concentration of sodium hydroxide = 0.50 M
We know that;
Number of moles = volume of solution × concentration of solution
Substituting values;
The number of moles of sodium hydroxide added = 0.9/1000 L × 0.50
= 0.00045 moles
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