Final answer:
The increasing order of acid strength for the compounds listed in series (a) is KH < AsH3 < H2Se < HBr, and for series (b) is H2SeO3 < H2SeO4 < H2SO4.
Step-by-step explanation:
The question asks for the order of increasing acid strength for two separate lists of compounds: (a) AsH3, HBr, KH, H2Se; (b) H2SO4, H2SeO3, and H2SeO4. Based on principles of chemistry, such as electronegativity and oxidation states, we can arrange these compounds accordingly.
For series (a), the acid strength typically increases with increasing electronegativity of the central atom, as well as the size of the atom in a period. Therefore, the correct order would be KH (being a metal hydride, it's the least acidic), followed by AsH3, then H2Se, and finally HBr (as Br is more electronegative than Se or As, and HBr is a strong acid).
For series (b), in oxyacids, the acid strength increases with a greater number of oxygen atoms (or higher oxidation state) and higher electronegativity of the central atom. Sulfur is more electronegative than selenium, hence H2SO4 is stronger than H2SeO4, despite having the same oxidation number of the central atom. However, H2SeO3 has fewer oxygen atoms than H2SeO4, making it the weakest among them. Thus, the correct order is H2SeO3 < H2SeO4 < H2SO4.