Answer
3.4 % (m/m) $K_2CO_3$
Work Step by Step
1. Write the expression for the mass percent:
$$Mass \space percent(m/m) = \frac{grams \space of \space solute}{grams \space of \space solution} \times 100\%$$
Mass of solution = Mass of solute + Mass of solvent
$$Mass \space percent(m/m) = \frac{ 26 \space g \space K_2CO_3 }{( 26 \space g + 724 \space g) \space solution} \times 100\%$$
Mass percent(m/m) = $3.4 \%$ (m/m) $K_2CO_3$ solution
