Question

why does the solubility of most solid substances in liquid solvents increase in temperature whereas gases reduce

Answer 1

For many solids the polar nature of the solid with that of water makes them more or less soluble. Remember like dissolves like and even organic compounds with not much polarity contain OH groups and that is similar to H2O. For gases dissolved in water, there is no such intermolecular forces. Oxygen, Nitrogen, etc are about as non-polar as you can get and there is just no interaction with a polar water molecule; at least what little interaction there is is weak. Hope this helps.