Because that is the ideal gas at STP.
I hope this will help you
Low pH = high acidity.
HF has a very low pH, so when added to a solution, it will lower the pH of the solution and therefore make it more acidic. So the answer should be B.
Exothermic reaction = the term exothermic process describes a process or reaction that releases energy from the system to its surroundings, usually in the form of heat, but also in a form of light, electricity,
Endothermic reaction = An endothermic process is any process with an increase in the enthalpy H (or internal energy U) of the system. In such a process, a closed system usually absorbs thermal energy from its surroundings, which is heat transfer into the system.
