What mass of magnesium hydroxide is required to create a 441 mL solution with a pH of 12.52?

How do i complete this electrolysis of water lab? i’m at home, so i don’t have the materials, and the lab didn’t properly work and was incomplete at school.

What prefix multiplier is appropriate for reporting a measurement of 5.57 ×10−5 m?

What is the empirical formula of a compound that is 50.7% antimony and 49.3% selenium ?