Answer:
Na^+
Explanation:
The symbol for sodium is Na. The term "sodium ion" assumes that the reader knows that sodium's single 3s electron is susceptible to theft by any nearby element that has a high electron affinity. Sodium's ionization energy is low, allowing the 3s electron to move elsewhere and leave behinf a positively charged Na^+ atom.
The given question is incomplete. The complete question is :
Which anion would bond with K+ in a 1: 1 ratio to form a neutral ionic compound?
a) 
b) 
c) 
d) 
Answer: b) 
Explanation:
For formation of a neutral ionic compound, the charges on cation and anion must be balanced. The cation is formed by loss of electrons by metals and anions are formed by gain of electrons by non metals.
Here potassium is having an oxidation state of +1 called as cation and thus is an anion must have an oxidation state of -1 if they have to combine in 1: 1 ratio to give neutral ionic compound.
Thus the anion has to be
which combines with
in 1: 1 ratio to give 
The Iron (III) ion is

The sulfate ion is

Thus when forming the compound iron (iii) sulfate you would need three sulfate ions bonded to two iron ions in order to fill the valency requirement
∴ the formula would be Fe₂(SO₄)₃
Whenever you are adding a number to a radical you must bracket it.
Substance 3 Is most likely to be a Metal for Its malleability and conductive properties.