42 grams of NaOH are needed to make a 250.0 mL or a 4.2 M NaOH solution (option C).
<h3>How to calculate mass?</h3>
The mass of a substance can be calculated by multiplying the number of moles by its molar mass.
However, the number of moles of NaOH can be calculated using the following formula;
Molarity = no of moles ÷ volume
no of moles = 0.250L × 4.2 = 1.05mol
Hence, the mass of NaOH can be calculated as follows:
mass = 1.05 mol × 40g/mol = 42g
Therefore, 42 grams of NaOH are needed to make a 250.0 mL or a 4.2 M NaOH solution.
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