What is depressant?

One of the following drug acts as depressant to our central nervous system.

What does depression of freezing point mean?How is the molecular mass of a non-volatile solute determined from depression of freezing point measurement?

2g of benzoic acid (C_(6)H_(5)COOH) dissolved in 25 g of benzene shows a depression in freezing point equal to 1.62 K. Molar depression constant for benzene is 4.9 K kg mol^-1 . What is the percentage association of acid if it forms double molecules (dimer) in solution ?

What is the relationship between depression in freezing point of a solution and molecular mass of the solute ?

What is the relation between depression in freezing point and molality of solute in the solution ?