Does a part or slice of a substance have a different density than the whole piece?

Pls help!

Alculate the concentration of h3o⁺in a solution that contains 5.5 × 10-5m oh⁻at 25°c. identify the solution as acidic, basic, or neutral.a) 1.8 × 10-10m, basicb) 1.8 × 10-10m, acidicc) 5.5 × 10-10m, neutrald) 9.2 × 10-1m, acidice) 9.2 × 10-1m, basic

Iknow the answer is a but i don't know why

If i make a solution by adding 83grams of sodium hydroxide to 750ml i’d water what is the molarity of sodium hydroxide