#"molarity"=("mol solute")/("liters of solution")#
The unit of molarity is #"mol/L"#, abbreviated #"M"#. You first need to determine the moles of salicylic acid #("C"_7"H"_6"O"_3")# in #"0.810 g"#.
Divide the given mass by the molar mass of salicylic acid #("138.122 g/mol")#. You can calculate the molar mass or look it up. Since molar mass is a fraction, #"g"/"mol"#, you can divide by multiplying the given mass by the inverse of the molar mass, #"mol"/"g"#.
#0.810color(red)cancel(color(black)("g C"_7"H"_6"O"_3))xx(1"mol C"_7"H"_6"O"_3)/(138.122color(red)cancel(color(black)("g C"_7"H"_6"O"_3)))="0.00586 mol C"_7"H"_6"O"_3"#
#"molarity"=(0.810"mol C"_7"H"_6"O"_3)/(1.00"L")="0.00586 mole/L"#
