Which molecule contains a polar covalent bond?

a)C2H4
b)ZnS
c)LiI
d)NBr3
e)AgI

Technically, both C2H4 and NBr3 have polar covalent bonds but most organic chemists don't consider the C-H bond to be polar.

To determine which molecule contains a polar covalent bond, we need to consider the electronegativity difference between the atoms in each bond.

Electronegativity is a measure of an atom's ability to attract electrons towards itself in a chemical bond. If there is a significant difference in electronegativity between atoms, the bond between them will be polar.

Let's examine the electronegativities of the atoms involved for each of the given molecules:

a) C2H4 (carbon and hydrogen) - Carbon has an electronegativity of 2.55, and hydrogen has an electronegativity of 2.20. The electronegativity difference is not significant enough for a polar covalent bond.

b) ZnS (zinc and sulfur) - Zinc has an electronegativity of 1.65, and sulfur has an electronegativity of 2.58. The electronegativity difference is not significant enough for a polar covalent bond.

c) LiI (lithium and iodine) - Lithium has an electronegativity of 0.98, and iodine has an electronegativity of 2.66. The electronegativity difference is significant enough for a polar covalent bond.

d) NBr3 (nitrogen and bromine) - Nitrogen has an electronegativity of 3.04, and bromine has an electronegativity of 2.96. The electronegativity difference is not significant enough for a polar covalent bond.

e) AgI (silver and iodine) - Silver has an electronegativity of 1.93, and iodine has an electronegativity of 2.66. The electronegativity difference is significant enough for a polar covalent bond.

Therefore, the molecule that contains a polar covalent bond is c) LiI (lithium iodide) and e) AgI (silver iodide).

To determine which molecule contains a polar covalent bond, we need to examine the electronegativity difference between the bonded atoms. A polar covalent bond occurs when there is a significant electronegativity difference between the atoms involved.

a) C2H4 (ethylene): Carbon and hydrogen have similar electronegativities, so this molecule does not have a polar covalent bond.
b) ZnS (zinc sulfide): Zinc and sulfur have different electronegativities, but this compound is ionic, not covalent.
c) LiI (lithium iodide): Lithium and iodine have significantly different electronegativities, so this molecule has a polar covalent bond.
d) NBr3 (nitrogen tribromide): Nitrogen and bromine have different electronegativities, so this molecule has a polar covalent bond.
e) AgI (silver iodide): Silver and iodine have significantly different electronegativities, so this molecule has a polar covalent bond.

Therefore, the correct answer is:
c) LiI
d) NBr3
e) AgI