1. What is 5% NaCl (m/v) solution means?
2. How would you separate a mixture of oil, sugar, and sand?

I don't know what the m/v means, you can either have a solution that is 5% by mass or by volume, normally it's by number of moles, which is related to the mass.

For 2, the sand and oil are immiscable in water, whereas sugar will dissolve, Oil is much less dense than water, whereas sand is denser than water.

Can you put these facts together to figure out a way to separate them?

m/v is mass volume percentage it describes how much solute in grams in 100mL of solvent. In this case 5% NaCl m/v means 5g of NaCl in 100mL of water or 10g of NaCl in 200g which equates to the same thing 5% :-)