If $11$ g of oxalic acid are dissolved in $500$ mL of solution (density= $1.1$\[g{\text{ }}m{L^{ - 1}}\] ) what is the mass % of oxalic acid in solution?
A.$1\% $
B.$2\% $
C.$3\% $
D.$4\% $

Hint: We can solve this question using the formula of mass% of solute which is given as-
$ \Rightarrow $ Mass% of the solute=$\dfrac{{{\text{Mass of solute}}}}{{{\text{Mass of solution}}}} \times {\text{100}}$
Here the solute is oxalic acid as it is dissolved in solution.
In the question, we are given the volume and density of the solution so we can find the mass of the solution by multiplying the volume and density of the solution. Then put all the values in the formula and solve it to get the answer.

Complete step by step answer:
Given, mass of oxalic acid=$11$ g
Density of the solution=$1.1$\[g{\text{ }}m{L^{ - 1}}\]
Volume of solution=$500$ mL
We have to find the mass % of oxalic acid in solution.
We know that mass% of solute is given by the formula-
$ \Rightarrow $ Mass% of the solute=$\dfrac{{{\text{Mass of solute}}}}{{{\text{Mass of solution}}}} \times {\text{100}}$
On putting the given values, we get-
$ \Rightarrow $ Mass% of the solute=$\dfrac{{{\text{11}}}}{{{\text{Mass of solution}}}} \times {\text{100}}$-- (i)
Since we are given the volume and density of solution we can find the mass of the solution using formula-
$ \Rightarrow $ Mass of the solution=$d \times V$ where d is the density of the solution and V is the volume of the solution.
On putting the given, values, we get-
$ \Rightarrow $ Mass of the solution=$500 \times 1.1$ g
On solving, we get-
$ \Rightarrow $ Mass of the solution=$50 \times 11$ g-- (ii)
On putting the value of eq. (ii) in eq. (i), we get-
$ \Rightarrow $ Mass% of the solute=$\dfrac{{{\text{11}} \times {\text{100}}}}{{{\text{11}} \times {\text{50}}}}$
On solving the above equation, we get-
$ \Rightarrow $ Mass% of the solute=$\dfrac{{{\text{100}}}}{{50}}$
On dividing the numerator by denominator, we get-
$ \Rightarrow $ Mass% of the solute=$2\% $

Hence the correct answer is option B.

Note:
Mass % is also written as w/w%. The concentration of solute can also be calculated in terms of weight by volume and volume by volume percentage in a similar way as we calculated the mass%.
The (weight by volume) w/v% is calculated as-
$ \Rightarrow $ w/v%=$\dfrac{{{\text{Mass of solute in gm}}}}{{{\text{Mass of solution in ml}}}} \times 100$
And v/v% is calculated using formula-
$ \Rightarrow $ v/v%=$\dfrac{{{\text{Volume of solute in ml}}}}{{{\text{Volume of solution}}}} \times 100$