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which statement best compares the solubility of these substances?
both substances are equally soluble at 30°c.
kcl will become less soluble at temperatures greater than 40°c.
kcl is more soluble at 20°c than nacl is.
both substances have the same solubility from 20°c through 40°c.

Explanation:

To answer this, one would typically refer to solubility - temperature graphs for KCl and NaCl. Solubility of most salts increases with temperature. For KCl, its solubility generally increases with rising temperature and doesn't decrease above 40°C. By referring to solubility data, at 20°C, NaCl is more soluble than KCl. And they don't have the same solubility from 20°C - 40°C. However, there are specific temperatures where their solubilities can be equal, and 30°C could be one such temperature if the solubility - temperature curves intersect there.

Answer:

Both substances are equally soluble at 30°C.