Step 1 - Understanding solubility of salts and gases
Solubility is the propertie of a substance to mix itself with another substance. It may happen in a lot of solvents, but we usually talk about solubility in water.
The solubility of a substance will depend on how strongly it interacts with water. In the case of a salt (such as LiCl) we can expect higher solubilities than in the cases of gases. That's because gases do not interact quite strongly with water.
Salts, on the other hand, may dissociate in water to form ions, which interact very strongly with water due to their charge. Not all salts are water-soluble though. It depends on some other features as well. But LiCl, as well as all chlorides (such as NaCl, KCl, and so on) are very soluble in water.
The solubility of salts usually increases with temperature (there are some expceptions to this general rule) whereas the solubility of gases decrease with temperature:
Step 2 - Using solubility to solve the problem
As we just saw, the solubility of a gas decreases with temperature, while the solubility of a salt increases with temperature.
H2 is a gas and LiCl is a solid (all ionic compounds are solid at room temperature), therefore we should expect that by warming the solution up to 75°C, the solubility of H2 will be decreased and of LiCl will be increased.
The result is that H2 gas will scape the solution and we'll see a lot of bubbles, whereas LiCl will remain dissolved in the solution. The correct answer is therefore alternative b) Gaseous H2 bubbles out of the solution.