. If a substance has an excess number of electrons on its surface, what type of charge does it have?
A positive charge.

A negative charge.

A neutral charge.

A nuclear charge.

A negative charge

Explanation:

If there is an excess of electrons in a substance, this will have a negative net charge. This is because electrons have negative charge

q = -1.67*10^{-19}

each electron will contribute with this charge to the total negative net charge of the substance.

hence, the answer is "A negative charge"

there are no contact forces mentioned on the list of choices that you've provided.