Answer:
1) RbClO4, Rb2CO3, Rb3PO4 2) Sr(ClO4)2 , SrCO3, Sr3(PO4)2 3) In(ClO4)3, In2(CO3)3, InPO4. Explanation :- To form a neutral compound with the given cations and anions, they must balance each other's charges for example if there is +1 charge on cati