240°C is required to dissolve 120 grams of KClO₃ in 300 g of water.
Explanation:
As per the solubility curve graph of different salts dissolved in 100 g of water, it can be noted that the KClO₃ gets saturated at 100 °C with the solubility of 59 g in it. But here the water is taken as 300 g and the salt is taken as 120 g. The graph shows the solubility of grams of salt in 100 g of water.
So, then we have to find what is the gram of salt present in 100 g of water for the present sample.
300 g of water contains 120 grams of salt.
Then, 1 g of water will contain 
g of salt.
Then, 100 g of water will contain 
of salt. This means, 100 g of water will contain 40 g of salt in it.
Then, if we check the graph, the corresponding x-axis point on the curve for the y-axis value of 40 g will give us the temperature required to dissolve the salt in water. So 80°C will be required to dissolve 40 g of salt in 100 g of water.
Then, in order to get the temperature required to dissolve 120 g in 300 g of water, multiply the temperature by 3, which will give the result as 80×3=240 °C.
So, 240°C is required to dissolve 120 grams of KClO₃ in 300 g of water.
