How many moles are in a 5m solution that has volume of 500ml

I am taking a guess that you mean 5 M solution instead of 5m, there is a different because M means molarity while "m" means molality.

molarity (M)= moles/ Liters

you can use this formula to solve for the moles

moles= Molarity x liters

molarity= 5 M

liters= 500mL= 0.500 L

moles= 5 x 0.500= 2.5 moles

note: if you did mean molality, let me know so I can edit the answer but it is actually the same answer.