What is the term for a ratio of equivalent measurements that can be used to change a value from one unit to another

Sodium sulfate dissolves as follows: na2so4(s) → 2na+(aq) + so42- (aq). how many moles of na2so4 are required to make 1.0 l of solution in which the na concentration is 0.10 m?

Are oil and water a mixture or solution

How many neutrons does an element have if its atomic number is 50 and its mass number is 166