Which of the following bonds is expected to be the most polar?

The polarity of a covalent bond is directly proportional to the electronegativity difference between the two bonded atoms.

The electronegativity values of the given elements on the Pauling scale are approximately:
$\text{C} = 2.5$
$\text{H} = 2.1$
$\text{N} = 3.0$
$\text{O} = 3.5$

Calculating the electronegativity difference ($\Delta \text{EN}$) for each bond:
$\text{C--H}: \Delta \text{EN} = 2.5 - 2.1 = 0.4$
$\text{C--C}: \Delta \text{EN} = 2.5 - 2.5 = 0$
$\text{C--O}: \Delta \text{EN} = 3.5 - 2.5 = 1.0$
$\text{C--N}: \Delta \text{EN} = 3.0 - 2.5 = 0.5$

Since the electronegativity difference is maximum for the $\text{C--O}$ bond, it is the most polar among the given options.

Answer: $\text{C--O}$