Chem MC

If for me, I will only choose 2 and 3 as ionic cpds. Explanations are as follows.
(1) AgBr. It can only be treated as an ionic cpd with strong covalent character. This is because, its cation carries a high charge density (with high polarizing power) due to its small size. The anion is thus strongly polarized by the cation due to its large anion size. As a result distorted anion is thus formed, leading to covalent character. AgBr doesn't dissolve in water also due to the covalent character.
(2)K2O. This is a normal oxide when potassium reacts with oxygen. The large size cation can hold the two oxygen atoms strongly by electrostatic attraction without imposing any distortion on their anion. Hence it can be treated as a pure ionic cpd.
(3)despite the transition metal zinc in the cpd, the electron-electron repulsion due to the fully filled 3d orbit makes it become large in size. Hence any distortion of anions (O2-) is thus prevented. It can be treated as an ionic cpd.
cpd = compound.
PS. The correct spelling of explainations is explanations
I hope you will find them helpful.

all of them are ionic compound
all of compound contain metal ion
Ag+ , K+, Zn2+

All of them are ionic compound.

Explainations:

Because all of them are ions bonded by strong ionic bond.

2007-04-27 17:06:46 補充：
my answer is for CE level