How many of the following compounds are acidic, alkaline or amphoteric (react with both acids and alkalis)?
A. Acidic = 10; Amphoteric = 2; Alkaline = 4
B. Acidic = 7; Amphoteric = 1; Alkaline = 5
C. Acidic = 9; Amphoteric = 2; Alkaline = 2
D. Acidic = 6; Amphoteric = 1; Alkaline = 6
E. Acidic = 8; Amphoteric = 1; Alkaline = 4
A trick to start with here is actually counting the number of compounds listed. In total, there are 13 compounds. Using this information, we can actually rule out A, as it accounts for 16 compounds.
We know that metal oxides are basic oxides, of which we need to choose those which dissolve in water- making them alkaline, with the exception of Al_2O_3, which is (1) amphoteric.
This puts us between B, D or E.
P_4O_{10} is an acidic oxide as it dissociates in water to give phosphoric acid.
MgO, Na_2O, K_2O, KOH are the basic oxides which form alkaline solutions in water. Hence, Alkaline= 4.
Our answer is E, and for safety you can review the remaining compounds and ensure they are acidic.