Calculate the concentration of a solution that is obtained by mixing $300\text{ g}$ of $25\%$ solution $\text{NH}_4\text{NO}_3$ with $150\text{ g}$ of $40\%$ solution of $\text{NH}_4\text{NO}_3$.

$30.0\%$

The correct answer is Option (2) → $30.0\%$ ##

Total mass of solution $= 300 + 150 = 450\text{ g}$

$\text{Amount of solute present in } 300\text{ g of } 25\%\text{ solution}$

$= 300 \times \frac{25}{100}$

$= 75\text{ g} $

Similarly,

$\text{Amount of solute present in } 150\text{ g of } 40\%\text{ solution}$

$= 150 \times \frac{40}{100}$

$= 60\text{ g} $

$\text{Total mass of solute} = (75 + 60) $

$= 135\text{ g}$

$\text{Concentration of solution (in \%)} = \frac{\text{Mass of solute in g}}{\text{Mass of solution in g}} \times 100$

$= \frac{135}{450} \times 100$

$= 30\% $