The unit of molarity is

The number of moles per litre, denoted by the unit symbol mol/L or $\mathrm{mol} {\mathrm{dm}}^{-3}$ in SI units, is the most often used unit for molarity.

Molarity (M) is a unit used to measure the concentration of a solution. It is defined as the number of moles of solute present in one liter (1 dm³) of solution. The formula for molarity is:

M=Volume of solution in liters/Number of moles of solute​

So, the unit of molarity is moles per liter, which can also be expressed as mol dm⁻³. The dm⁻³ (decimeter to the power of -3) is equivalent to liter because 1 liter is equal to 1 cubic decimeter (1 dm³).

• mol stands for moles, which is the amount of substance.
• dm⁻³ represents the volume of the solution in decimeters cubed (equivalent to liters).

Explanation of the other options:

• a) mol: This only represents the amount of substance, but it does not account for the volume of the solution, so it can't be used as a unit for molarity.
• b) mol⁻¹: This suggests the inverse of the number of moles, which is incorrect for molarity.
• d) mol kg⁻¹: This is the unit of molality, not molarity. Molality is defined as the number of moles of solute per kilogram of solvent, not per liter of solution.

Thus, the correct unit for molarity is mol dm⁻³, which tells you how many moles of solute are present in each liter (or decimeter cubed) of solution.