The pair of elements that forms a bond with the least electronegativity difference is1 pointK and ClO and ClNa and ClMg and Cl

To answer this question, we need to know the electronegativity values of the elements mentioned. Electronegativity is a measure of the tendency of an atom to attract a bonding pair of electrons. The Pauling scale is the most commonly used. Here are the approximate values:

• Potassium (K): 0.82
• Chlorine (Cl): 3.16
• Oxygen (O): 3.44
• Sodium (Na): 0.93
• Magnesium (Mg): 1.31

Now, let's calculate the difference in electronegativity for each pair:

• K and Cl: 3.16 - 0.82 = 2.34
• O and Cl: 3.16 - 3.44 = 0.28 (absolute value)
• Na and Cl: 3.16 - 0.93 = 2.23
• Mg and Cl: 3.16 - 1.31 = 1.85

The pair with the least difference in electronegativity is O and Cl.