Idon't really understand how to figure this out.
select the compound that is paired with its correct type of bonding.
h2o: nonpolar covalent bond
zncl2: polar covalent bond
cl2: nonpolar covalent bond
ch4: polar covalent bond

Cl2

Explanation:

Cl2 is a covalent molecule because it contains 2 non-metal elements.

It is non-polar because both elements have the same level of electrostatic attraction (remember that electrostatic attraction is the tendency to steel an electron from an element with lower a  lower electrostatic force)

In Cl2 since there are only 2 molecules that are the exact same there is no overall dipole (which means that one end of the molecule is slightly positive or negative charge)

If the molecule replaced one Cl or something else then it would be non-polar since one element will be more electrostatic than the other and one region of the molecule will have a slightly positive or negative charge, unless the molecule is symmetrical like CH4.

For CH4 (methane) if you drew this as a lewis structure the Carbon would be surrounded by 4 hydrogen atoms meaning the overall dipole will be cancelled out since the molecule is symmetrical.

You may not understand the last part but just know that:

If there are 2 of the same atoms in the molecule (Cl2) then it is non-polar

If there are 2 non-metals then the bond is covalent

Water is always polar