It is normally a colorless solution in water. It is a strong oxidizing agent. It can turn into selenium trioxide when dehydrated carefully. It is a very strong acid. It reacts with hydrochloric acid to make chlorine and selenous acid. It can dissolve gold to make gold selenate. When heated above 200°C, it releases oxygen and turns into selenous acid. It reacts with bases to make selenates.
Selenic acid is made by oxidation of selenium dioxide with hydrogen peroxide. It is hard to evaporate it, but when it is evaporated, it makes colorless crystals. It can be made by oxidation of selenous acid with a strong oxidizing agent, such as potassium permanganate, chlorine, or bromine. The HCl and HBr made as a byproduct can reduce the selenic acic to selenous acid again, though, so it has to be taken out.