Final answer:
The oxidation number of calcium in Ca(HSO4)2 is +2. This is concluded by knowing the typical oxidation numbers for hydrogen and oxygen and using the rule that the sum of oxidation numbers must be zero for a neutral compound.
Step-by-step explanation:
To determine the oxidation number of calcium in Ca(HSO4)2, start by using the known oxidation numbers of other elements and work by established guidelines. We know from guideline 3 that hydrogen has an oxidation number of +1. With oxygen assigned an oxidation number of -2, we calculate sulfur's oxidation number using guideline 4, which requires that the sum of oxidation numbers must equal the charge of the compound.
Firstly, the compound Ca(HSO4)2 is neutral, so the sum of oxidation numbers should be zero. Calcium typically has an oxidation number of +2. Now, for each hydrogen sulfate (HSO4-), hydrogen is +1, and with four oxygens each at -2, the total for oxygen is -8. To balance this in a way that the overall charge of the hydrogen sulfate ion is -1, sulfur must have an oxidation number of +6.
As for the calcium ion Ca2+, its oxidation number is directly +2 by rule 2. Therefore, the oxidation number of calcium in Ca(HSO4)2 is +2.