Final answer:
The charge on the niobium ion in Nb2O is +1, since each oxide ion has a charge of 2-, and there's one oxygen atom, making the 2 niobium ions need to balance the charge with +2 in total, or +1 each. Correct option is C.
Step-by-step explanation:
The charge on a niobium ion in Nb2O can be determined by considering the charges on the oxygen atoms in the compound. Oxide always has a 2- charge. As there's just one oxygen atom in Nb2O, the total negative charge is -2. Since the compound is electrically neutral, the two niobium ions together must balance this with a positive charge. Thus, each niobium ion would have a charge of +1 to make the total positive charge equal to +2 which balances the -2 charge from the oxide ion. Therefore, the correct answer is C. Positive one.